The Mark 27 Mod 4 torpedo was a submarine-launched acoustic torpedo designed by the Ordnance Research Laboratory of Pennsylvania State University in 1946 as an improved version of the Mark 27 torpedo. Fully compatible with electrical setting fire control systems through the use of the standard 65-pin umbilical cable, this weapon was in service on submarines for about ten years. It was withdrawn from service use in 1960 with the introduction of the Mark 37 torpedo.