 The term "M4" can refer specifically to the initial sub-type with its Continental radial engine, or generically, to the entire family of seven Sherman sub-types, depending on context.Many details of production, shape, strength, and performance improved while in production, without a change to the tank's basic model number.These included stronger suspension units, safer "wet" (W) ammunition stowage, and stronger or more effective armor arrangements, such as the M4 "Composite", which had a cheaper to produce cast front hull section mated to a regular welded rear hull.