from: www.amcm.org/prelude.html

Prelude to Operation ENDSWEEP

By AD1 Barry W. Marple  USN Retired

Imperceptibly at first, the lull in the air war over North Vietnam came to a progressive end during the last two months of 1971 and the first quarter of 1972.  The North Vietnamese, seeking to hide preparations for their new offensive against South Vietnam, began firing more frequently at reconnaissance aircraft and their escorts flying "Blue Tree" missions, and the U.S. responded with more and heavier protective reaction strikes.

As increased evidence of an incipient North Vietnamese offensive was being gathered and as the Paris Peace Talks were stalemated, the United States broke off the negotiations on 23 March 1972.  Furthermore, not wanting to be caught unprepared as they had been four years earlier when the Communists launched their 1968 Tet Offensive, South Vietnamese and American forces went on full alert.  Thus, when three North Vietnamese Army (NVA) divisions, including tanks and heavy artillery supported by a large number of shoulder-fired SA-7 surface-to-air missiles, crossed into South Vietnam on 30 March to initiate the 1972 Spring Offensive, the defenders were ready on the ground and a schedule to bring air reinforcements had been detailed.  For Task Force 77 (TF 77), this meant that its aircraft were immediately thrown into the battle to provide much needed air support to the South Vietnamese defenders (680 sorties were flown during the first week of April as opposed to an average of sixty-six weekly sorties during the previous quarter) while plans were made for a new air offensive against the North.

Already intense, the pace of activity increased even further in May as the scope of U.S. air operations over the North was broadcast with the launching of Operation Pocket Money and Linebacker.  On 10 May, restrictions on sustained air operations above the 20th parallel were lifted as Operation Freedom Train gave place to Linebacker 1.  On 18 May, bombing of several industrial targets in the Haiphong restricted zone were first authorized.  From the Naval Aviation point of view, however, the most significant event was Pocket Money, the mining campaign against all major North Vietnamese harbors and waterways, which was announced by President Nixon on 9 May.  Simultaneously with this announcement, in which a three-day warning was given to enable Soviet and neutral merchant vessels to leave North Vietnamese waters before the mines were activated.  A-6As and A-7Es from CVW-15 sowed the first sixty-six mines (with 72-hour arming devices) in the outter approaches of Haiphong Harbor.  Two days later, six other harbors were mined and soon thereafter mining operations were extended to include most coastal and inland waterways.  Eventually, over an eight-month period, more than 11,000 mines were planted, effectively blockading maritime transport to and from North Vietnam.

At last, on 23 January 1973, the hollow but grandiloquently titled Agreement on Ending the War and Restoring the Peace in Vietnam was signed in Paris.  In accordance with the Agreement, preparations for the return of the prisoners of war (Operation Homecoming) were made, the removal of mines from Haiphong Harbor (Operation ENDSWEEP) was scheduled to commence within a month, and air operations over both North and South Vietnam were to end.  Offensive operations against the North had been suspended on 15 January, and all other air activities over North Vietnam ceased on 23 January.  The last sorties over South Vietnam were flown on 27 January but not before two more aircraft were lost.  The pilot and bombardier / navigator of a VA-35 A-6A from USS America were recovered by a Navy helicopter on 24 January, thus becoming the last of 161 Naval Aviators rescued by Navy SAR helicopters.  Cdr. H.H. Hall and LCdr. P.A. Kienzler, the pilot and RIO of a VF-173 F-4J from USS Enterprise, the last Navy aircraft to be lost in combat during the Southeast Asia War were taken prisoner of war after ejecting on 27 January but were soon released.

Planning for Operation ENDSWEEP had begun before the conclusion of the Paris Peace Talks as, knowing that the mining of Haiphong was having telling effects on the North Vietnamese economy, the U.S. negotiating team had used an offer of removing the mines as a bargaining point to obtain from Hanoi the release of American prisoners of war.  Accordingly, as soon as negotiations were concluded, the Navy set up Task Force 78 (TF 78) to conduct minesweeping operations in North Vietnamese waters using surface minesweepers and specially configured CH-53 helicopters from one Navy and two Marine Corp squadrons (HM-12, HMK-463, and HMM-165) which operated from the deck of two amphibious assault ships, USS Inchon (LPH-12) and USS New Orleans (LPH-11).  Mine removal operations began on 6 February and ended on 27 July 1973.  During that time, USS Coral Sea, USS Enterprise, USS Oriskany, and USS Ranger were sent at various times, to the Mine Logistics Carrier Station to provide air cover for TF 78.  However, the most important contribution made to Naval Aviators during Operation ENDSWEEP was that made by the crews from the three helicopter squadrons which flew over 1100 hours on mine removal duty.

On 20 June 1973, five-weeks before Operation ENDSWEEP was completed, Congress ordered the cessation of all combat operations in Southeast Asia on 15 August.  Although the congressional action effectively ended U.S. participation in the Southeast Asia War, fighting continued in Vietnam and Cambodia.

For U.S. personnel, the relief brought by this unconclussive end to their fighting was bittersweet as nothing could be shown for the sacrifices and suffering of so many.  While serving with TF 77, three hundred and seventy-seven Naval Aviators had been killed in action, 144 of the 179 aircrewmen known to have been taken prisoner of war were returned by the North Vietnamese, and at least 99 others were still reported as missing in action.

from: www.amcm.org/nortwick.html

Operation Endsweep


by LtCol John Van Nortwick  USMC

The unique experience of the 1974 CMC Aviation Efficiency Trophy Winner, HMH-463, during Operation Endsweep, are recalled by the squadron's former CO LtCol John Van Nortwick.  Marine helicopters implemented the Navy-developed Airborne Mine Countermeasures program in Haiphong Harbor.  A former enlisted man, LtCol Van Nortwick received his wings in 1956.  He holds a master's degree from the University of Southern California

The following article, which was featured in the May 1974 issue of Marine Corps Gazette, is reprinted with permission of the Author LtCol John Van Nortwick.


"ENDSWEEP"
by LtCol John Van Nortwick

The Marine Corps implements a Navy-developed
countermeasures technique to clear enemy harbors
of mines - using the heavy helicopter.


The Navy Sea Mine has been
successfully used many times
since the Civil War to control
strategic sea areas.  In October
1952, the landing of the First
Marine Division in Wonson,
North Korea, was delayed for
six days by 3,000 mines laid by
a technically unsophisticated
force in sampans and small
boats.
The mining of North Vietnamese
ports in 1972 by Seventh Fleet
attack aircraft led by Marine
A-6's provides a further excellent
example of the value of mining
operations. It is acknowledged
that these operations hastened the
settlement of the Vietnamese War.

(pic no longer available)

My personal observation of the apparent importance to the North Vietnamese of subsequent U.S. mine clearing operations only reinforces the strategic importance of the sea mine.

Soviet, Soviet Bloc, and Chinese Communist Navies all maintain an active minelaying capability. The Soviet Navy has over 100 ships of various classes with this capability. Bloc nations such as Egypt, Cuba, and North Vietnam also maintain a similar capability with Soviet assistance. The Chinese Communist Navy is self-sufficient in this area with the ability to deploy minelaying destroyers and corvettes to Western Pacific areas of strategic importance quickly.

To counter this threat the Navy has developed the Airborne Mine Countermeasures (AMCM) program which transfers the surface mine clearance or countermeasures operation to an airborne platform, specifically the helicopter.  The helicopter tows various devices thru the water of a minefield.  These devices un turn cause the magnetic influenced mine and the acoustic mine to detonate in place.  In the case of the moored contact mine, the device cuts it from its anchor allowing the mine to rise to the surface where it is detonated by small arms fire.  A detailed discussion is found in the inner portion of this article.  Concurrent with the development of the mine countermeasures helicopter has been the attainment of a world-wide quick reaction capability.  RH-53D or CH-53D helicopters, AMCM tow systems, and support personnel can be rapidly airlifted by C-5A to specific strategic areas considerably faster than previous surface mine warfare forces could deploy.

The concept of using helicopters for Airborne Mine Countermeasures originated during the Korean conflict when Navy helicopters were used to spot mines.  As a result, the Bureau of Aeronautics undertook the exploration of the tow capability inherent in rotary wing aircraft.  The earliest feasibility studies and tests, conducted with the HRP-1 helicopter in the early 1950's, concluded that a suitable configured helicopter could perform well as a towing vehicle and that AMCM was a feasible concept.

The promise shown by these early successes led to the establishment of the U.S. Naval Air Mine Defense Development Unit (NANDDU) with a mission to assist the Bureau of Aeronautics in the development and evaluation of airborne equipment and tactics for all aspects of AMCM.  The functions of this unit were later assumed by the U.S. Naval Coastal Systems Laboratory.

After further studies, tests, and demonstrations, the SH-3A helicopter, modified to an AMCM configuration (RH-3A), was approved for service use as the first operational minesweeping helicopter.  RH-3A helicopters assigned to the fleet in 1965 were capable of operating from two dedicated AMCM support ships.  As new minesweeping equipment was developed, the performance limitations of the RH-3A were exceeded and the RH-53D and the CH-53D were selected as replacement helicopters for the primary and emergency minesweeping missions.

The development of an airborne acoustic and magnetic minesweeping capability so enhanced the AMCM concept that in 1970 the Chief of Naval Operations directed action to affect a transition from a surface dominated MCM force to one principally utilizing AMCM helicopter units operating from suitable support platforms.

In April 1971, a helicopter squadron, Helicopter Mine Countermeasures Squadron Twelve (HM-12), was commissioned at Norfolk, Virginia, and tasked with a primary mission of worldwide AMCM.  The squadron functions under the operational control of Commander, Mine Warfare Force, Charleston, South Carolina.  Initially, HM-12 was equipped with CH-53A's on loan from the Marine Corps.  The helicopters were brought up to CH-53D specifications by Sikorsky Aircraft Corporation prior to commencing AMCM operations.  The squadron is now equipped with the RH-53D, the primary minesweeping helicopter.

Operation Endsweep
In the later part of 1972 it became apparent that the Vietnam War would end and that the clearance of U.S. - laid mines from North Vietnamese waters would be required.  Major elements of the Mine Warfare Force, including Mobile Mine Command (MOMCOM), Mine Warfare Support Group (MWFSG), and HM-12 were airlifted by C-5A to NAS, Cubi Point, Republic of the Philippines.  These Navy mine warfare experts formed the nucleus of Task Force 78, under the command of RAdm Brian McCauley, for this unique operation to be known as OPERATION ENDSWEEP.

As the scope of the operation was realized, the need for additional helicopter assets became apparent.  Responding to the Navy request for assistance, CG FMFPAC directed that HMH-463 deploy from MCAS Kaneohe Bay, Hawaii, to NAS, Cubi Point, to join Task Force 78.  On 27 November, 1972, with the efficient support of Col Bill Crocker's MAG-24, the pineapple people of 463 embarked at Pearl Harbor aboard USS Inchon (LPH-12), which was en route from Norfolk to augment Seventh Fleet Amphibious Forces and to participate in ENDSWEEP.

After a crossing highlighted by shipboard qualifications for all pilots HMH-463 arrived at  Cubi on 9 December 1972.  Representatives from MAG-36, 1st MAW and TF 78 met the squadron and assisted in preparing for the unique mission.

The remainder of December and the first three weeks of January 1973 were spent awaiting direction from higher authority while the Paris Peace Talks continued.  However, on 15 January 1973, activity picked up when HMH-463 was directed to modify all squadron aircraft to the AMCM role.  On 26 January 1973, authority to commence actual AMCM training was received, and the squadron, with assistance from HM-12, developed and carried out a training program for its own crews as well as the CH-53D crews from two composite squadrons, HMM-154 and HMM-165, of Col Bill Maloney's MAG-35.  In the short period between 26 January and 14 February, approximately 50 pilots and 50 crewmen each received at least three magnetic pipe training flights.  During this period, HMH-463 formed an AMCM detachment of three CH-53D's, eight pilots, and thirty-six maintenance personnel.  It embarked on the TF 78 flagship, USS New Orleans (LPH-11) in support of HM-12.  This detachment participated in a mine exercise in Subic Bay until 13 February, when due to a change in task organization, they cross-decked to USS Cleveland (LPD-7) to form AMCM unit Delta where they were operationally controlled by Cdr Mel Ronzo of the MOMCOM staff.  Three CH-53D's of HMM-165 were then placed in support of HM-12.  Simultaneously, the remainder of HMH-463 reembarked upon their old friend, USS Inchon, commanded by Capt. J.K. Thomas.  The squadron, with six CH-53D's formed AMCM unit Charlie under the direction of Cdr Dan Powell of MOMCOM.  The remaining three embarked CH-53D's were dedicated to the support of Detachment Delta aboard Cleveland.  Joining the squadron at this time was a detachment of six CH-46D's and two UH-1E's of HMM-164 to provide utility and rescue functions.

AMCM units Charlie and Delta conducted a successful minex in Subic Bay 16-23 February to polish their newly learned AMCM skills, and sailed on 26 February aboard Inchon and Cleveland to join TF 78 in Haiphong Harbor on 28 February.  The task force was made up from a sizable portion of WestPac Navy assets, two LPH's, three LPD's, two DD's, two LST's, four MSO's, and numerous auxiliaries and support vessels.  Marine aviation units, other than HMH-463, were HMM-165, commanded by LtCol Doc Egger and later, LtCol Bruce Colbert; and Detachment HMM-164, whose OiC's were Maj Bill Simmons and Maj Dave Amey.  Additionally, many individual Marines were involved in public affairs, photography, and liaison.  Senior Marine on the TF 78 staff was LtCol Carroll Redman, who was later relieved by LtCol Vic Lee.

Anxious to begin the operation after months of delay, both Marines and sailors were again to be disappointed.  Political considerations at higher levels delayed commencement of AMCM operations until 12 March.  However, the waiting period was well spent.  The aircrews used the time to polish their instrument flying skills.  This practice proved to be a real asset because of the marginal weather later encountered in the area of operations.

On 12 March, AMCM unit Delta (Detachment Delta, HMH-463) commenced magnetic and acoustic minesweeping operations in the Lach Huyen area of Haiphong Harbor.  To keep one CH-53D sweeping in the minefield continuously from dawn until dusk, it was necessary to launch a half-dozen three-hour sorties per day.  Generally, Detachment Delta, under its able OIC, Capt Ron Rensch, flew three or four of these sorties, the remainder were flown by HMH-463 crews from Inchon.

A typical minesweep sortie began with the towing of the magnetic pipe from the LPD to the minefield under radar control, approximately a 30-minute evolution.  At this time, radar coverage from the LPD was lost and the actual two-hour sweep was conducted by pilot judgment utilizing previously prepared charts.  A 30-minute return to the LPD followed.  If operational planning was correct and no mechanical difficulties were encountered, an incoming relief helicopter passed the outgoing one at the minefield boundary.  Five days after the initial start in Haiphong Harbor the squadron was totally committed when authorization to commence sweeping the channel to the Port of Hon Gai was received.  The managerial talents of HMH-463's operations officer, Maj Bruce Shapiro, and aircraft maintenance officer, Capt Ernie Noll, were taxed to meet each day's schedule.  While still providing two or three sorties a day in support of Detachment Delta, now located about twelve miles away, the squadron launched several three-hour sorties into the Hon Gai minefield utilizing an entirely different procedure.  It involved externally lifting the magnetic pipe and acoustic device from the number seven spot of the LPH flight deck, carrying it some ten miles to the minefield vicinity, hovering and streaming the pipe and device in the water behind the helicopter.  This operation took about fifteen minutes and was followed by a two and one-half hour sweep in the minefield and then a reversal of the entry procedure followed by a return flight to the ship.  Control in this field was accomplished by radar using TACRON controllers on board a mine sweeper near the field.

During this period, HMH-463 was flying over 200 per cent of CNO utilization on a daily basis.  This sustained high performance was achieved thru the efforts of such professionals as Capt Don Dugan, squadron maintenance control officer, and CWO-2 Don Cavinder, squadron material officer, the many fine Marines under them, and particularly, the CH-53D crew chiefs and first mechanics.

It is important to note that the CH-46D's and UH-1E's of HMM-165 and Detachment HMM-164 were providing valuable admin and utility support to the task force, including daily flights into the North Vietnamese airfield at Cat Bi.  HMM-165's three CH-53D's were also providing AMCM support to HM-12 and gained valuable experience with the MARK 105 Seaborne Equipment Platform.  The updated CH-53A's of HM-12 were conducting MARK 105 AMCM operations from two LPD's located in other parts of Haiphong Harbor.

On 26 March, the Lach Huyen field was completed and the detachment's assignment was shifted across Haiphong Harbor to the vicinity of the Do Son Peninsula.  Sweeping continued until 1 April when Inchon and Cleveland departed Haiphong for a routine upkeep period in Subic.  While there, the squadron performed much needed heavy aircraft maintenance and even took a day or two off.  Returning to Haiphong on 15 April and expecting to finish the job, HMH-463 was unhappily surprised when TF 78 sailed into the Tonkin Gulf and approximately a week later returned to Subic.  Again, the Task Force was a victim of higher level political requirements.  What followed was a two-month period of uncertainty while diplomatic maneuvering continued.  Many changes took place within the Task Force.  USS Tripoli (LPH-10) replaced New Orleans as flagship, Cleveland returned to Long Beach and was relieved by Dubuque (LPD-2), necessitating that Detachment Delta cross-deck to this latter ship.  Personally, the most significant change was my relinquishing command of HMM-463 to Maj Bill Smith on 5 June.  During this period, also, Capt Art Sifuentes took over a demanding and important assignment as OiC, Detachment Delta.

On 14 June, TF 78 was directed to resume operations.  HMM-463, now embarked on Inchon and Ogden after yet another detachment cross-deck move, arrived in the Hoi Gai area on 20 June.  It commenced operations to complete the Hoi Gai Channel and commenced a new field located further north near Cam Pha.  A third minesweeping technique was used in this area.  The triple magnetic pipe which consisted of three pipes towed in tandem and trailed some 2,700 feet behind the helicopter was utilized.  In this case, the air-to-air transfer method was used to maintain one CH-53D sweeping at all times.  The first sortie of the day towed the triple pipe in the field and at the end of three hours transferred the tow line to the relieving helicopter thru the use of a marker float and grappling hook procedure.  This was continued throughout the sweep day and the triple pipe was returned to the ship by the last sortie.

HMH-463 completed the Hon Gai and Cam Pha fields on 26 June and proceeded to Vinh, the next assigned area.  Sweeping in this area commenced on 28 June and was completed on 3 July.  Inchon returned to Haiphong once more for an additional assignment until mid-July when it returned to Subic.  At this time HMH-463 was directed to cross-deck to Ogden and Dubuque, for the return trip to Hawaii.  This was accomplished in approximately twelve hours and on 21 July the main body of the squadron departed Subic for Hawaii.  On 1 August 1973, the pineapple people of HMH-463 arrived at MCAS Kaneohe Bay, Hawaii, and on 2 August 1973, the Navy announced that Operation ENDSWEEP was officially over.  The three helicopter squadrons involved, HMH-463, HMM-165 and the Navy's HM-12, towed mine clearance devices over 27,000 miles, more than the circumference if the earth, while logging over 2,000 hours of tow time.  HMH-463 flew approximately half of these totals.

Summing it up, Operation ENDSWEEP was unique in many ways.  Entirely new techniques were quickly and efficiently mastered.  The CH-53D again proved its worth as it had in the past.  Marine aircrews proved themselves capable of meeting new challenges.  Finally, the frustrations of working in a sensitive political atmosphere were experienced.  In total, Marine Aviation delivered when it was asked to.

Current status
The sea mine threat to amphibious operations is easily envisioned.  To
combat this threat, the Navy has
converted from a surface mine countermeasures force to an airborne
one. However, it is entirely conceivable
that Marine Aviation will be requested
to assist in mine clearance operations in support of amphibious operations in the future.  Therefore, it is important to look
at our capability.  The Commandant has stated that the Marine Corps will
continue to provide emergency AMCM support during amphibious operations
when requested.  However, no formal training program exists at this time and
the AMCM expertise gained by Marine Aviation during Operation ENDSWEEP
is rapidly being lost as time and transfers take their toll.

An analysis of the total AMCM system is required in order to determine future Marine Corps actions needed to maintain an emergency readiness capability.  The AMCM system is made up of the following five subsystem.

Trained personnel
Aircraft
AMCM Helicopter Modification Kits
AMCM Tow Systems
Operating Platforms
Trained Personnel
The subsystems of trained personnel is divided into pilots and crewmembers, tow systems operators, support personnel, and command and control personnel.

(pic no longer available)

HMH-463 pilots and crewmembers rapidly learned the fundamentals of AMCM.  The average pilot was considered qualified after three flights of three-hour duration each, and the average crewman after five such flights.  This initial success, however, should not be construed as an indicator of future training requirements for the following reasons:

Prior to the commencement of flight operations many hours were spent in the classroom learning the theory of AMCM and becoming familiar with AMCM tow systems and the CH-53D modification kits.

(pic no longer available)

Crew chiefs were responsible for the modification of their assigned aircraft and became thoroughly familiar with all AMCM equipment through practical application.
The AMCM tow system used exclusively by HMH-463 was the magnetic pipe, a 30-foot, 1,000 pound buoyant pipe which required minimum maintenance and no systems operation during sweep operations.
Coordination between pilots and crewmen during AMCM operations is of prime importance.  This coordination was not fully present until many tow hours in Haiphong Harbor had been flown.  The squadron gained its experience on the job.
The only AMCM training syllabus currently in use is presented in Charleston, South Carolina, and Norfolk, Virginia, by HM-12.  The pilot AMCM syllabus consists of a five-day ground school at Charleston which covers airborne mine warfare familiarization and is followed by AMCM flight training in Norfolk, Virginia. This flight training consists of eight, three-hour training sorties.  It introduces pilots to all AMCM modification kits and tow systems and the procedures involved in their use from both shore and ship.  A shipboard minex occurs during this phase to familiarize pilots with shipboard procedures.  The AMCM flight syllabus covers procedures for streaming, towing, and recovering the tow systems as well as for air to air, air to ship, and ship to air transfers of the systems.  It also covers emergency procedures.

The crewmember AMCM syllabus consists of a two week ground school in Charleston which covers airborne mine warfare familiarization and aircrew procedures for AMCM tow systems.  This is followed by AMCM flight training at Norfolk.  This flight training consists of fifteen, three-hour AMCM training sorties.  It introduces crewmembers to all AMCM modification kits and tow systems and the procedures involved in their use from both shore and ship.

Consideration should be given to maintaining a nucleus of AMCM trained pilots and crewmembers in HMH squadrons.  It is acknowledged that this would have relatively low priority in view of other commitments, however, a minimum number of trained personnel could quickly qualify the remainder of an AMCM committed HMH squadron should the requirement arise.

(pic no longer available)

Tow systems operators
The five AMCM tow systems require from one to four crewmen in addition to the helicopter crewchief in the aft cabin compartment depending upon which system is employed.  Training requirements to deploy, operate, and recover these systems range from moderate for the magnetic pipe (MOP), to extensive for Mark 103 moored minesweeping system.  Crew and training requirements are shown below:


Crew requirements have changed since 1974  SYSTEM CREW REQUIRED TRAINING
MK-103 4
Extensive
MK-104 2
Moderate
MK-105 1
Extensive
MK-106 1
Extensive
MOP 2
Moderate

At this time, no information is available which indicates whether Navy or marine tow systems operators will be utilized during future Marine supported AMCM operations.

In view of the complexity of the systems, and the emergency only role of the Marine CH-53D's, the employment of Navy tow systems operators is desirable in order to provide rapid response to future operational requirements.

Support personnel are those designated to provide technical assistance and to maintain AMCM tow systems and associated equipment.  In view of the fact that this equipment is relatively complex and is in Navy custody until needed, personnel of the Mine Warfare Support Group (MWFSG) will provide the necessary support.

Command and control of all Operation ENDSWEEP helicopters was provided by Navy personnel from Mobile Mine Command and Tactical Control Squadron Eleven utilizing a variety of techniques.  These techniques included:

Navigation by a precise navigation system (raydist) installed in the AMCM helicopter and dependent upon signals from four shore based antennas.  Political considerations limited its use to only the Haiphong main ship channel.  This system would not be usable unless adjacent terrain was controlled by friendly forces.
Navigation by radar control utilizing the fire control radar of the supporting LPD to position the AMCM helicopter to correctly enter the minefield.  At this time radar contact was lost and minesweeping was conducted by the freelance method utilizing pilot judgment.  This method required additional sorties to insure maximum clearance due to the accuracy criteria developed by mine warfare planners.
Navigation by radar control from surface minesweepers (MSO) positioned adjacent to the minefield.  This method proved most satisfactory from the standpoint of system reliability and accuracy of sweep tracks.
At this time there is no way to predict the adjacent terrain characteristics or the peculiar features of any future minefield.  However, any of the above methods or any combination of or variation on them may be utilized.  It is important to understand that flexibility and ingenuity are valuable assets that future mine warfare planners will use.

Statistical minesweeping is a complex and time-consuming operation that must be meticulously planned by an experienced mine warfare staff and then conducted as precisely as is possible.  For these reasons Marine units committed to minesweeping will be under the operational control of a Navy command with the necessary mine warfare planning expertise.

The RH-53D is the primary mine countermeasures helicopter.  However, all Marine CH-53D's now have the required airframe changes to accept AMCM modification kits and AMCM tow systems.  The modification of CH-53D helicopters during Operation ENDSWEEP proceeded smoothly and presented no problems.

Tow systems
The helicopter modification kits are of two basic types-the tow kit and the streaming winch kit.  The tow kit contains the necessary parts, assemblies, and components to accomplish two of the six tow missions.  The helicopter equipped only with the tow kit is utilized for Mark 105/106 and triple pipe operations.  The tow kit includes provisions for an amber/red selection of the underside rotating beacon required by NATO agreement for tow helicopters; automatic flight control system interconnections to provide automatic cable yaw angle retention, and aircraft attitude and heading hold, and adjustable rear view mirrors with controls for both the pilot and copilot.  A combination tensiometer, cable yaw angle indicator with an adjustable automatic cable release is also provided.  The instrument features an adjustable high and low limit warning light.  The tow boom transmits the tow load to the airframe through the range of zero to 20,000 pounds and can be extended to permit rotation of the bellmouth, release of the hook retention maws, and lowering of the hook using the cargo winch cable.  The tow hook is provided with pilot controlled electrical release and crew operated manual release systems as well as an adjustable automatic release.  Guillotines, which are pilot actuated, accomplish emergency release in the event of hydro-electrical system malfunctions.  A dam is provided to restrict water entry into the cabin in the event of a water landing prior to closing the lower ramp.  Guide rollers attached to the end of the lower ramp and upper ramp door hinge area protect the airframe and tail rotor from inadvertent damage from cables.

The streaming winch kit contains a twin winch installation with each winch separately controlled by a crewman.

The helicopter equipped with both the tow kit and the streaming winch kit is utilized for Mark 103/104, and single magnetic pipe operations.  An emergency shut-off capability is provided for both winches by a single control switch on either winch.  The winches are hydraulically powered by the aircraft utility hydraulic system.  In addition, streaming rollers are provided to restrict cables within the aircraft, protecting the area so that crewmen can carry out their duties.

There are five AMCM tow systems.  They are the Mark 103 moored minesweeping system, the Mark 104 acoustic minesweeping system, the Mark 105 influence minesweeping system, the Mark 106 influence/acoustic minesweeping system, and the AMCM magnetic pipe in various combinations and configurations.

The Mark 103 moored minesweeping system contains a complete right hand and left hand sweep system.  Racks are installed on both sides of the aircraft providing stowage of the sweep gear, including cutters.

(pic no longer available)

The equipment consists of a depressor, otters or paravanes, and floats, all interconnected with cable.  These cables are the tow cable, sweep wire, and float pendants.  Cartridge-actuated cutters are spaced along the sweep wire.  There are ten cutters per sweep wire leg, and four legs making a total of 40 cutters.  The Mark 103 can be used in several assembly variations.  For instance, Assembly 01 is the entire sweep, that is, all four legs.  Assembly 03 may be half a set with both legs on one side. These are all tactically useful configurations that can be used as the operational situation dictates.

The Mark 104 acoustic minesweeping system consists vehicle and the necessary cradles for inflight stowage.  A davit is used to lift the vehicle in and out of the cradle.  Polypropylene tow cable on storage drums is used with the streaming winch to deploy the Mark 104 acoustic system.

(pic no longer available)

The Mark 104 acoustic minesweeping system consists of vehicle and the necessary cradles for inflight stowage.  A davit is used to lift the vehicle in and out of the cradle.  Polypropylene tow cable on storage drums is used with the streaming winch to deploy the Mark 104 acoustic system.

The major components of the Mark 105 influence minesweeping system is the seaborne equipment platform.  The equipment platform consists of the floats which provide the basic structure for the hydrofoil elements, the buoyancy, and the fuel containers; the power pack which is a small gas turbine engine; the wing, which supports the power pack; connects the floats, and supports the sweep boom; the lifting or retrieval rig; and the foils.  The foils contain upper and lower foils in the front.  The lower foil and the aft foils are sub-cavitating foils.  The upper foils are super-cavitating and are used primarily in rough seas.  The sweep boom is the support for the tail and electrodes.  The platform is towed by the helicopter in the basic tow configuration.

When the Mark 104 acoustic device is attached to the Mark 105 magnetic minesweeping device the combination is referred to as the Mark 106.

AMCM magnetic pipe

(pic no longer available)

This device is a 30-foot pipe, weighing 1,000 pounds, having a 10 3/4-inch diameter filled with polystyrene foam.  The pipe has a plate at each end to make the device watertight and may be towed from either end.  The pipe is given a magnetic charge prior to each sweep mission.

Three magnetic pipe combinations exist. They are:

Magnetic Pipe/MK-104. The MK 104 is connected astern of the pipe with a 25 foot nylon line.
Magnetic Pipe/MK-2 (G). The MK-2 (G) acoustic device (rattle-bars) is connected astern of the pipe with a 12 foot nylon line.
Triple Magnetic Pipe.  Three magnetic pipes are connected in trail with 800 foot nylon lines.  This combination trails 2,700 feet behind the towing helicopter.
All CH-53D AMCM tow system combinations may be operated from either LPH or LPD shipping or from a shore base with one exception.  The triple pipe must be towed either from the stern gate of an LPD or from a shore base.  The LPD is the preferred platform from which to support AMCM operations.  However, its utilization in this role severely hampers its ability to support simultaneous amphibious operations.  The reasons for this are:

The flight deck is 100% dedicated to AMCM operations.
The well deck is not available approximately 1 1/2 hours prior to Mark 105 or magnetic pipe launch and 1 hour after recovery.
During launch and recovery operations, the ship is restricted in speed and direction.
Although the LPD is generally preferable, alternate utilization of the LPH as a support platform for all but the triple pipe will free LPD's to provide amphibious support.

This review of AMCM would not be complete without addresal of of the areas of logistics, vulnerability and operational planning.

The concept of logistics support to AMCM units is unchanged from that to any other unit with one exception.  AMCM equipment, both CH-53D modification kits and AMCM tow systems, occupies considerable space on board amphibious shipping.  Planning and coordination must be made early with ship's personnel to insure sufficient space is made available, particularly if other aviation units or ground units are embarked.

Vietnam taught us that the low-flying, slow-moving helicopter is extremely vulnerable to enemy action.  AMCM helicopters operate at 125 to 150 feet at speeds below 20 knots.  They possess no defense capability other than two .50 caliber machine guns and are incapable of maneuver to escape destruction.  Therefore, it is paramount to plan early for the provision of adequate means to insure their survivability.  These means include:

Neutralization of the amphibious operation area.
Attainment of air superiority
On station combat air patrol and close air support aircraft.
Escort by helicopter gunships.
Naval gunfire support.
Use of smoke, terrain, or weather to mask operations.
Operational planning for AMCM operations is detailed and must begin as early as is possible.  Mine warfare force personnel must be co-located with the HMH as soon as possible to mesh all the components of the AMCM system into a cohesive and coordinated AMCM unit.  Continuous coordination with higher, adjacent, and supporting commands is maintained to provide efficient and effective AMCM planning, preparation, and training.

This review has shown that the majority of the assets required to conduct successful emergency AMCM operations in the future are available on a routine basis within the Marine Corps and Navy.  The only critical shortcoming is lack of AMCM trained Marine pilots and crewmembers.  This deficiency can be overcome through the utilization of existing training programs and facilities.

from: www.history.navy.mil/wars/vietnam/minenorviet.htm

U.S. Mining and Mine Clearance in North Vietnam
By Edward J. Marolda

During the Rolling Thunder bombing campaign (1965-1968), the U.S. Navy's carrier air squadrons released thousands of mines along the enemy's key supply routes in the "panhandle" area of North Vietnam. The object of the operation was to make vehicular and other movement around ferry crossing sites, railway and highway bridges, storage areas, truck parks, and fuel dumps difficult if not prohibitive for the enemy. Carrier attack aircraft also "seeded" inland waterways and roads used by the Communists to transport munitions into Laos and South Vietnam. The weapons used were Mark 36 Destructors, which contained 500 pounds of explosives and detonated when trucks, tanks, or other metal objects disturbed their magnetic fields. Neither the Navy's mining effort nor the overall bombing campaign stopped the flow of munitions to the fighting front but they forced the enemy to devote scarce resources to defense of his supply line.

Another mining operation, which the Navy carried out during 1972 and early 1973, had an even greater impact on the war. Early on the morning of 8 May 1972, aircraft carrier Coral Sea (CVA 43) launched three Marine A-6 Intruders and six Navy A-7 Corsair attack planes toward the coast of North Vietnam. Shortly afterward, the naval aircraft laid strings of thirty-six 1,000-pound Mark 52 mines in the water approaches to Haiphong, through which most of North Vietnam's imported war material and all of its fuel supply passed. During succeeding months, other carrier aircraft dropped thousands of mines and 500-pound, Mark 36 Destructors in the seaways of North Vietnam's secondary ports and "reseeded" the Haiphong approaches.

For the remainder of 1972, twenty-seven Sino-Soviet bloc merchant ships chose to remain immobile in Haiphong rather than risk a transit of the mined waters. The mining campaign, along with U.S. air attacks on North Vietnam's supply lines ashore, helped cut short the enemy's "Easter Offensive" in South Vietnam. Eventually, the mining operation and the Linebacker bombing campaign induced the North Vietnamese to negotiate an end to the war.

On 27 January 1973, American and North Vietnamese officials signed a protocol to the Paris agreement that called for the United States to neutralize the mines that the Navy had dropped in North Vietnam's coastal and inland waterways.

On 28 January, following months of preparation, Rear Admiral Brian McCauley's Mine Countermeasures Force (Task Force 78), of the Seventh Fleet, deployed from Subic Bay in the Philippines to Haiphong. To coordinate actions, on 5 February Commander Task Force 78 met in the city with his North Vietnamese opposite, Colonel Hoang Huu Thai. Operation End Sweep began the next day, when ocean minesweepers Engage (MSO 433), Force (MSO 445), Fortify (MSO 446), and Impervious (MSO 449) swept waters off the coast near Haiphong. Guided missile frigate Worden (DLG 18) and destroyer Epperson (DD 719) stood by in case the North Vietnamese tried to interfere with the effort. Later that month, amphibious ships New Orleans (LPH 11), Dubuque (LPD 8), Odgen (LPD 5), Cleveland (LPD 7), and Inchon (LPH 12) joined the task force. On board the newly arriving ships were 31 CH-53 Sea Stallion helicopters from the Navy's Helicopter Mine Countermeasures Squadron 12 and from Marine helicopter squadrons HMM-165 and HMH-463. The Sea Stallions towed minesweeping sleds and other devices. During the six months of Operation End Sweep, 10 ocean minesweepers, 9 amphibious ships, 6 fleet tugs, 3 salvage ships, and 19 destroyer types operated in Task Force 78.

The helicopters swept the main shipping channel to Haiphong on 27 February and the ports of Hon Gai and Cam Pha on 17 March. In early April, Commander Task Force 78 deployed to the formerly mined waters MSS 2, a decommissioned LST filled with buffer material and crewed by volunteers. The ship carried out eight passages of the Haiphong channel to make sure no mines remained active in the vital waterway. Elsewhere in North Vietnam, U.S. Navy technical personnel prepared 50 North Vietnamese sailors to conduct their own minesweeping operations. While this was taking place, a number of U.S. C-130 transport aircraft delivered minesweeping gear to Cat Bi Airfield outside the city. Until 17 April, the Navy task force continued its mission. Then, because Hanoi failed to carry out its obligations under the Paris agreement, Washington ordered a suspension of minesweeping operations. End Sweep resumed on 18 June when American leaders were persuaded that the North Vietnamese would once again act in good faith. Shortly afterward, Admiral McCauley notified the North Vietnamese that the ports of Haiphong, Hon Gai, and Cam Pha were free from the threat of American-laid mines. Next, Task Force 78 concentrated on the coastal areas off Vinh. Finally, on 18 July 1973, McCauley led his flotilla out to sea, officially ending Operation End Sweep.


--------------------------------------------------------------------------------

Sources:

Marolda, Edward J. By Sea, Air, and Land: An Illustrated History of the U.S. Navy and the War in Southeast Asia. Washington: Naval Historical Center, 1994.

Marolda, Edward J., ed. Operation End Sweep: A History of Minesweeping Operations in North Vietnam. Washington: Naval Historical Center, 1993.

Schreadley, Richard L. From the Rivers to the Sea: The U.S. Navy in Vietnam. Annapolis: Naval Institute Press, 1992.

.