M4 Sherman medium tank, armed with a low-velocity 75mm main gun. The tank sports extra welded armor on its hull.  

Sherman tank

Subcaliber firing was used by the U.S. Army to develop a tank gunner's accuracy, speed, and confidence without the costs and disturbance of firing the main armament. In general, the coaxial machine gun was used for the subcaliber training.

However for fire adjustment training, a standard submachine gun was mounted outside the tank. Until a standard mount could be developed, the Tank Gunnery manual recommended the following mount for the 75-mm gun on the M4. For firing, the submachine gun was connected to the firing solenoid from the coaxial machine gun. 

July 10, 1944

Gunnery Training

An American M10 tank destroyer works its way through the rubble of a French town in the summer of 1944.