Production Order T-8348: 75 units: Serial Number 43453/USA 3099687 through S/N 43527/USA 3099761
The US Medium Tank was designed around a modified 9-cylinder Wright
R-975 Whirlwind radial aircraft engine that was widely used by the Army
Air Corps and had a proven record of reliability. As the US military
commenced its massive build up in the early 1940s, materials priority
appears to have been given to the Navy and Air Corps. Recognizing that
there would be a critical shortage of aircraft engines, the Army turned
to the automotive industry for alternate tank power plant designs. In
July 1941, just as M3 Medium production was getting underway, the
Ordnance Department asked the Chrysler Corporation if it could design an
alternate medium tank engine "in a hurry." The expedient that emerged
used the "off the shelf" 6-cylinder engine from Chrysler's "Royal" line
of automobiles and combined five of them into a "star" configuration.
The Army found Chrysler's unconventional "stop gap" design acceptable,
and in December 1941, the Ordnance Department contracted for the
installation of 109 "experimental multiple engine power plants" in the
Medium Tank, M3. This configuration was given the nomenclature "M3A4"
and approved for production later that same month. The 109 M3A4s were
manufactured from June through August 1942. This was not a simple engine
swap. The massive "Chrysler Multibank" required an 11-inch elongation
of the existing hull. Despite numerous teething problems and the
complexity of the 30-cylinder Multibank engine, the Government committed
its flagship Detroit Tank Arsenal to the Multibank's continued
production and in early January 1942 Chrysler was contracted to build
the third T6 (Sherman) pilot. It would be a welded hull model, elongated
for the Multibank, and given the nomenclature "M4A4." For a sense of
the chronology, we would observe that the M3A4s were immediately
replaced in production by the M4A4s, with the first 2 accepted in July,
followed by 167 in August 1942. The pilot M4A4, Serial Number 3, USA
3058315 is shown above. It was completed on 9 May 1942 and delivered to
Aberdeen Proving Ground later that month. In a side view such as this,
the 10-inch gap (1) between the road wheels is a good recognition
feature of the elongated M4A4 hull. On the "as designed" Sherman hull,
the gap is about 3 inches. This applied to all of the other models - M4,
M4A1, M4A2 and M4A3.