A 3/4 view of the M2a4 - note hull sponson .30-caliber MGs and bow-mounted step. THe two horizontal bars on the glacis were to deflect bullets from bouncing off the hull into the driver's compartment.
It pioneered a number of features found on later US tanks, including:
a. A rotating turret armed with a tank-killing 37mm gun (which also had anti-personnel capabilities) and a co-ax .30 mg
b. An air-cooled, gasoline-powered radial engine adapted from an aviation engine for high power and light weight
c. A vertical volute suspension system
d. A hull-mounted flexible .30 caliber mg operated by the co-driver
e. A pintle-mount .30 mg for the tank commander
This AFV was, at the time it was constructed, both swift and mechanically-reliable, and armed with a potent 37mm gun the equivalent of (and based on) the German PAK 35/36 gun, also in 37mm caliber - so it could have held its own in combat in 1940.
A pre-production M2A4 on display at USA Aberdeen Proving Grounds in Maryland in 1939
However, the real importance of this vehicle was that it was used as the direct basis of the following tanks:
1. M2 Medium - it was the M2A4 on steroids, with the same basic layout, the same suspension (just more of it, as it was longer), a larger radial engine, the same 37mm gun and the same .30 caliber MGs (but a lot more of them); and,
2. M3 Light Tank (dubbed "Stuart" by the Brits), which was basically the same vehicle, with a bit more potent engine, thicker armor, a different gun mount for the 37mm cannon, and a trailing idler to provide greater ground contact and floatation for the tracks, to absorb the added weight of greater armor.
The M2A4 was indirectly responsible for (through the M2 Medium) the M3 (British name Grant/Lee) and the M4 (Brit-name Sherman), both of which had the same mechanical layout as the M2 Medium - suspension, drive train, engine, etc.
The M2A4 was also indirectly responsible for the M5 light tank (also Brit-named Stuart), the M8 GMC with a 75mm howitzer, a whole range of high-speed tractors, the Brits' turretless M3/M5 "Kangaroo" APCs used in NW Europe, and (via turrets) several of the gun- and howitzer-turreted LTV Amtrak amphibious landing craft.
However, the greatest direct influence of the M2A4 was the M3 series of light tanks which were direct extenders of the M2A4 design, with just a few changes to the gun mount, the idler wheel and internal features. The M3 quickly evolved, losing the fixed-hull machine guns and adding lots of stowage (most externally), but it always remained an upgraded M2A4.
An operational M2A4 with what looks like a cloth temporary tactical recognition band. Also note how the turret hatch would naturally reflect bullet strikes into the vehicle commander's face - ouch!
- Bow-on view of M2A4 in operational service
- There were only 375 M2A4s built - Britain ordered a batch, but only 36 were made before the contract was shifted to the more potent and capable M3 light tanks. Not clear if this was 375 + 36, or 375 including 36. Rumor has it that the Brits shipped the M2A4 to Egypt, but then shipped them on to India where they (were rumored to) saw combat against the Japanese Army 4th Armored brigade.
Profile view of production M2A4
The Brits received 36 M2A4 tanks - here's one (named Al Capone) being examined by Royal Armored Corps technicians
However, it is substantiated and documented that the USMC took some M2A4 light tanks into combat on Tulagi and Guadalcanal, beginning with the invasion of those two islands on August 7, 1942. They did see combat, in units which also contained M3s. It's not clear if they saw head-to-head combat with Japanese light and medium tanks (some Marine tanks did fight them in the battle of Matanikau River on Oct. 23rd, 1942, but I can't confirm that the M2A4s were in this fight.
Side view of Marine M2A4 during Guadalcanal campaign
USMC M2A4 leading a pair of USMC M3 light tanks at Guadalcanal, summer/fall, 1942 - the only time US forces took the M2A4 into combat (some may have been based at islands that were attacked by air strikes, but that's not the same thing as taking them into battle).
There is a resin kit/conversion of the M2A4 - I've got one ordered from Poland, but have no idea when or if it will arrive - but if you want to model an obscure but seminal early-war tank, the M2A4 should be in your list.