There were three major variants of the H-1, the Bell model 204, 205 and 212.
Bell model 204
XH-40 : ( later redesigned XHU-1 ) The Bell Model 204 first flown in October 1956 with one 700 hp turbine engine. The 3 prototypes built were the first turbine engine aircraft of the US Army. ( serial number 55-4459 )
YH-40 : ( later redesigned YHU-1 ) 6 test units with a fuselage 30 cm (1 feet) longer
HU-1 : ( with the normalization of 1962 became the UH-1 Iroquois ) 9 pre-productions units with one 770 hp T53-L-1A tested during 1959
HU-1A : ( later UH-1A ) 173 units produced up to March 1961. A crew of 2 plus 5 troops.
TH-1A : 14 UH-1A converted to dual control trainers
UH-1B : 1014 units built between 1961 and 1965 with a 960 hp T53-L-5 engine. 7 troops
UH-1C : 750 units with the same fuselage of the UH-1B but a larger engine (L11) and a newer rotor system that give them much greater manoeuvrability
UH-1E : 192 units built between 1964 and 1966. Was the UH-1B/C for the US Marines for assault support with salt-water corrosion protection and extra avionics. 8 troops.
TH-1E : 20 trainers of the UH-1E variant
UH-1F : ( also called UH-48 as missile site support helo ) The UH-1B variant for the USAF with a 1300 hp T58-GE-3 turbine engine. 119 units built from 1964 to 1967. 10 troops
The UH-1F had a General Electric engine rather than the Lycoming engine used on other models at the time. It was more powerful than the Lycoming engines until the Lycoming TH-53-L13 engine was introduced in mid 1967.
TH-1F : 26 UH-1F trainers
HH-1K : The UH-1E for the US Navy for SAR duties with a 1400 hp engine. 27 units in 1970
UH-1L : The UH-1E for the US Navy for multi-purpose duties with a 1100 hp engine. 10 units in 1968
TH-1L : 90 trainers for the US Navy
UH-1M : 3 UH-1C updated with a 1100 hp engine and 6 french AS.11 anti tank missiles for evaluation. They had a different rotor system and the tailboom had a sweeping vertical fin.
UH-1P : 20 UH-1F updated for psycological warfare
AB.204 : Model 204 built by Agusta in Italy
Fuji 204B-2 : Model 204 built in Japan
Bell model 205
YUH-1D : 7 prototypes ordered in July 1960 with a larger main rotor and a bigger fuselage for a 12 / 14 troops capacity
UH-1D : 2000 units with a 1100 hp turbine engine. First unit enter service in August 1963
UH-1H : The most important variant of the Huey was an updated version of the UH-1D with a 1400 hp T53-L-13 engine. 4900 units built for the US Army and 50 countries
EH-1H : UH-1Hs modified for electronic warfare in variations EH-1H Phase A and B and the UH-1X Model. Were replaced with the Sikorsky EH-60A
HH-1H : 30 UH-1Hs for the USAF for combat / SAR duties
The modification included moving the tail rotor to the right hand side of the tailboom. This modification was picked up by the US army and later UH-1H type aircraft were configured with the tail rotor on the left side.
UH-1V : 200 UH-1Hs modified for medevac duties in the 80s
AB.205 : Model 205 built by Agusta in Italy
Fuji 205 : Model 205 built in Japan
Bell model 212
UH-1N : After the successful of the Models 204 / 205, Bell joined Pratt & Whitney Canada for develop a twin engine derivate of the UH-1H to achieve a specification came from the Canadian Armed Forces. The result was the Model 212 Twin Two Twelve adopted by the USAF (79 units ) and the US Navy / Marines ( 221 units)
VH-1N : 8 units Marine One for the US president.
UH-1Y : Remanufactured UH-1N
AB.212 : Model 212 built by Agusta in Italy, including the AB.212 ASW naval helicopter
This is a great web site with pictures.
www.globalsecurity.org/military/systems/aircraft/uh-1-pics.htm