If you are too old to go in as a line officer, you get to choose Limited duty officer....can anyone here splain this to me in detail?  Thanks in advance for your help.  

ARMY

I could be wrong but IIRC, from my Navy experience: LDO's are useless and Line Officers are even more useless.

All kidding aside, LO's can go on to command, LDO's are more or less pigeon-holed into a speciality, like running the mess hall, depot maintenance, etc.  LO's need to be constantly moving up the ranks or they will become either LDO's or civilians.

thanks!

Okay...here is the straight skinny from a retired LDO (Line), U. S. Navy:

The Limited Duty Officer program was set up decades ago to provide technical support to unrestricted line officers.

All Naval officers can be grouped into two broad catagories:  Line and Staff.

Line officers are further divided into unrestricted and restricted line catagories.  Unrestricted line officer are surface warfare officers (ship drivers) who may command a ship...except a carrier or a sub, aviators, who may rise to command an aviation squadron and eventually a carrier, and submariners who go on to command subs.  

Restricted line officers include SeaBees and certain other specialized communities.  Staff officers are intel weenies, lawyers, doctors, dentists, nurses, etc.

Limited Duty Officers (LDOs)are line officers OR they are staff officers, depending on what their commissioning source rating was.  LDOs who are commissioned from enlisted ratings like fire control, boatswain mate, gunners mate, or engineman, are commissioned as LDO Line officers.  A legalman or yeoman would be commissioned as a Chief Ship's Clerk staff officer.  A hospitalman would be commissioned as a [staff] medical services officer.  Get the picture so far?  It is complicated and it does get confusing...even for an old fart like me.

LDO line officers are eligible under the law to command certain types of ships.  This might include a sub support vessel or a sea going tug.

LDO line officers, while not strictly required to work for and get their Surface Warfare qualification like their unrestricted brethren, often do.  In so doing, they are then fully qualified to act in the COs stead on any ship, when he is absent from the bridge underway and the ship while inport.  I almost got my ship underway from anchorage due to heavy weather while all the more senior officers were ashore.  Fortunately the seas abated and the wind lessened and we rode it out at a short anchor stay.

Finally, LDOs are commissioned either as ensigns in the regular Navy if they selected while serving as an E-6 first class PO, OR if they have already served a few years as a Warrant Officer and attained the rank of CWO-3.

Chief Petty Officers are automatically commissioned as CWO-2.  They can later move up to be LDOs if they wish.

Got it?

They are line officers...but NOT unrestricted guys like Naval Academy or ROTC.  All were formerly enlisted...with many years of experience in their chosen field.

[soapbox]