Four seats, three seats, no seats in the turret
Loader vs autoloader, and the unmanned turret bet.
The four-man Western crew
Commander fights the tank. Gunner makes the shot. Loader feeds the gun and covers a sector with a machine gun. Driver gets them there. The loader is also a spare brain: map, radio, wounded evacuation, road wheels. U.S., German, and British designers kept him because ammunition in a bustle with blow-off panels is safer than a carousel underfoot.
The three-man autoloader
T-64 started it; T-72, T-80, T-90, and Leclerc continued. Rate of fire is consistent (not faster than a good loader in the first ten seconds, faster after that). The cost is well-known: a hit on the carousel tends to throw the turret (“jack-in-the-box”). Leclerc’s bustle autoloader tries to have it both ways.
Unmanned turrets
T-14 puts all three crew in a hull capsule. The turret is a remotely operated gun. In theory this is the next survivability step. In practice it demands cameras that work when dirty, electronics that survive jamming, and factories that can build it. Until those exist at scale, the four-man composite turret is still the Western default.