The engine compartment provide some key identifying features which the M4 shares with the M4A1, i.e. :
Rear hull :
* twin access doors,
* air cleaners at the top outer corners of the doors,
* twin square muffler tailpipes at the top of the rear hull above the air cleaners
Rear deck :
* steel-covered air intake behind the turret
* solid engine access doors behind the air intake
You can make out some of these features on the picture below showing a
late-production M4 from the Detroit Diesel Arsenal (with a hybrid cast/welded hull).
Since the tank shown
here is a welded hull Sherman, it is either an
early-production M4 or a
mid-production M4.
Either way, it remains an
M4.
