In May 1944, the production of the M4A2 switched from the
75mm main armament to the new M1A1 76mm gun.
As the M1A1 didn't fit into the old turret a new one was developed, called T23, and the new commander's copula became standard.
The ammuniton storage changed to »wet«, so the characteristic 1-inch side armour plates of the »dry« storage could be omitted.