The U.S. Army finally has a new light tank, the 38-ton MPF (Mobile Protected Firepower) vehicle. MPF has not yet received a customary name as the 55-t0n M1 Abrams or 15-ton M551 Sheridan. Both of these looked like tanks but the M1 was a major success while the M551 was not. The army takes its time deciding such mundane matters as official names for new tanks. Obtaining a new light tank is a process that began over 30 years ago just before the M551 was retired from combat service. Some M551s continued to serve as a simulated enemy tank in large scale training exercises at the NTC (National Training Center) until 2003. There were a lot of M551s still available because 1,662 were built between 1966 and 1970. The M551 failed in combat. It had a crew of four and a unique 152mm gun that used twenty onboard 152mm short range shells or nine Shillelagh guided missiles with a max range of 3,000 meters. The 152mm gun was never very reliable and during its only combat experience (Vietnam 1969-72) performance of the M551 and its 152mm main gun were dismal. The M551 152mm gun was unreliable and only used shells in Vietnam to supply infantry with much needed fire support. Only 200 M551s were sent to Vietnam and most were destroyed by enemy fire (RPG rockets or heavy machine-guns) or broke down during use. The 155mm gun had a slow rate of fire and had only 24 shells on board if missiles were not carried. There were often problems with the fire control system. The army came up with several modifications but gave up on the M551 by 1978. The 82nd airborne division kept using them because they could be dropped by parachute and still function.
The U.S. Army didn’t look for an M551 replacement until 1992 and the first candidate was the M8 Buford Armored Gun System, which was to replace the M551 in the 82nd Airborne Division and in several other units. The M8 was developed in 1983 using corporate funds and used several innovations to produce a well-protected 24-ton tracked vehicle with a 105mm high velocity gun using an autoloader. That meant a crew size of three. The autoloader was based on the one the Navy had been using for its Mk 54 five-inch (127mm) gun. The M8 autoloader allowed up to twelve shells a minute to be fired. The M8 design was accepted in 1992 and mass production was to begin within four years with the first M8s entering service in 1997. Severe and unexpected cuts in the army budget led to the abrupt cancellation of the M8 in 1996 in order to prevent manpower cuts involving 20,000 troops. The M551 was also retired in 1997
The army still wanted a light tank and in 2002 adopted a limited (142) number of the 19-ton M1128 Stryker Mobile Gun System, which also used an autoloader for the 105mm gun and could fire ten rounds a minute. This autoloader was of a slightly different design than the one in the M8. When the M1128 was airdropped, there were problems with the autoloader. Without the airdrops the 8x8 wheeled M1128 was successful in combat (Iraq) and the army planned to produce a lot more but that idea was dropped in 2012 when it was decided to seek a heavier tracked vehicle as the replacement for the M551. That led to the MPF, which adopted many of the techs that worked in the M8 and M1128. One item not adopted for MPF was the autoloader. The main reason for that was the MPF uses a version of the M1 tank 120mm gun and fire control system in a turret based on the one used in the M1.
Western nations have avoided autoloaders for their heavy tanks. The only exception was the French LeClerc heavy tank, which was designed to fire the same 120mm ammunition as the M1 and Leopard 2 tanks. Unlike the Russian T-72, the LeClerc autoloader does not require leaving the ammunition in the crew compartment. France designed the tank around the autoloader, rather than having to design the autoloader to fit into the tank, as was the case with the T-72. The LeClerc autoloader was a success but no other Western nation has adopted the French approach, yet.
Russia pioneered use of autoloaders in the 1960s with their T-64 tank and that was successful enough to include it in the T-72 and all subsequent Russian tanks. Russian autoloaders look like a carousel. When it is time to load the 125mm gun, the carousel swivels to the ready position, and the cassette with the round and propellant bag is aligned with the main gun’s chamber. The cassette gets lifted up, and the main round is rammed in first, followed by the propellant charge. The gun then fires, and the process is repeated for the next round. This is a system that has the benefit of working well with the compact Russian tank designs. It has allowed Russia to field a lot of tanks and to keep them in the field due to the elimination of one member of the crew.
The Russian autoloader was not as well-designed as the later French autoloader or the earlier one used in the M8. The Russians skimped on providing at least one item of safety gear that was inexpensive and great for crew morale. It’s initial lack of a cheap slide-up metal shield meant the autoloader would occasionally load the gunner’s arm. The autoloader in the T-64/T-72/T-80/T90 also stores the ammunition in the crew compartment and that means that if one of those shells goes off in the turret (because of enemy fire or an accident), the crew dies and the tank is lost. Eventually the Russians added that safety feature for the gunner and improved reliability of the autoloader but nothing was done to get the ammo carousel out of the crew compartment. That led to the loss of a lot of T-72s, T-80s and T-90s in combat, spectacularly so in Ukraine during the first months of the 2022 Russian invasion.
Most Western tanks continue to use a human loader. The rate of fire is slower; a round every ten seconds from an M1 compared to one round every three seconds from a LeClerc, or one round every 6.5 seconds from a T-72. The use of a human loader allows Western tanks, especially the M1 and Leopard 2, to keep the ammunition away from the crew compartment. This is often the difference between a crew getting killed and a crew surviving, even if the tank is a total loss.