For about four years now, there's been an M1A3 version of the American M1 tank in the works. One of the most contentious aspects of this new model is the reduction of the crew from four to three. Despite the fact that about half the tanks on the planet use three man crews, this is seen as a major obstacle to overcome for Western tanks. It's all about workload and catering to the needs of the tank.
The M1A3 model would be a radical upgrade, compared to previous ones. One goal is to make the 62 ton M-1A2 a few tons lighter. This would involve a lightweight 120mm gun, which would allow for the installation of an autoloader, new fiber optic wiring, and new (and lighter) armor. A new engine and running gear would also save weight. The M-1A3 might get down to 55 tons, or less.
But the most important changes would be the new computers, communication, sensors and navigation gear intended for the unrealized FCS tank. The FCS vehicle was to use new heavy weapons, that fire guided projectiles to a range of 12 kilometers. These can also be mounted in the M-1A3, along with an autoloader in the turret. This eliminates the need for human loader. Autoloaders have been used in tanks for about half a century. The Russians pioneered the use of this device in their tanks, but for over a decade, they had serious problem making the damn thing work reliably.
These days, only one Western tank, the French LeClerc, has an autoloader, and it is deemed reliable enough. So putting such a device in the M1A3 is not seen as technically impossible. Cutting the crew size to three is another matter. That's because the smaller crew has caused a lot of problems where it has been used. The most immediate problem is maintenance. Tanks require constant maintenance by their crews. This extends from checking, and sometimes doing something to, the mechanical components every day. The tracks (that the tanks move on) have to be checked constantly for wear or damage. You don't want a track falling off in combat, especially if you could have caught the defective link and done something about it beforehand. The wheels, which move the tracks, have components that have to be lubricated regularly, and checked for wear or damage. Then there's the engine, weapons and other mechanical devices. Modern tanks are full of electronics that have to be put through self-checks, as well other bits of fussing about necessary to keep electronics in top shape.
When the tanks halt in a combat zone, the crew has to check the exterior, and do some cleaning (to knock crud, like mud, or debris, out of the tracks and make sure the engine exhaust is clean). In desert areas, there are dust problems. Filters have to be checked, and you definitely want to take good care of the air conditioning system.
After you halt for the night, some of the crew will be needed for guard duty, but now you have 25 percent fewer crewmen for this duty. The obvious solution for this is to transfer all, or some, of the unneeded crewmen to a maintenance support unit in the tank company or battalion. Currently, American tank battalions have 350 men, and about 62 percent of them are members of four man tank crews. Working out exactly how this new personnel distribution will be implemented, will take time. While that is happening, the tanks will be less well maintained, the crews will be overworked and the effectiveness of the units will be lower.