[Would you like to see this in-game?]
TL;DR: A T12 GMC halftrack captured and used by Japanese troops.
After observing the numerous advantages motorized anti-tank weapons had during the French campaign in 1940, the US came to the conclusion that if they were going to effectively take out new armored threats, they were going need a dedicated self-propelled gun built on a decently capable platform and armed with a powerful cannon. The platform choses would be the new M3 halftrack, a derivative of the M2 halftrack. The M1897A4, an American modernized development of the old French Canon de 75 modèle 1897, was chosen as the main armament. The new SPG would be constructed in June, 1941, and was designated T12 Gun Motor Carriage. This new SPG was very simple in design and construction. A 75mm cannon, fitted with a small and simple gunshield, placed at the front of the former troop compartment was all it was. The vehicle would undergo and pass trials, performing remarkably well considering how quickly it was developed, before entering service in August, still designated T12 and still in the configuration it underwent trials in. (It wasn’t until a new gunshield was installed that the vehicle was designated M3 GMC). Only 6 months after the T12 had been designed, it was thrown into the fires of war, seeing its first action in the Philippines when the Japanese invaded. This would lead to the mass capture of American equipment by the Japanese. Among said equipment was several T12s, which the Japanese would later use against the US in defense of the Philippines. The T12 would also be featured in a Japanese wartime propaganda newspaper about captured equipment.
Low-tier non-tech tree options are always in short supply when it comes to Japan as just about anything indigenous, one-off half-functional prototype or not, almost needs to be in the tech tree. The T12 GMC could provide Japanese Rank I a premium or squadron vehicle that isn’t a the crappy Ha-Go or the expensive Ro-Go… While the vehicle itself would could be considered “copypaste” it’s playstyle would still be different from any tech tree vehicle. It’s decent mobility combined with the fantastic 75mm APHE slinger and good reload would make for some great and familiar low-tier fun. As previously stated, the best placement for this vehicle is as a Rank I premium or squadron vehicle as the vehicle was captured.
Armament: 75mm M1897A4 cannon
Dimensions: 6.24m 2.22m, 2.49m (L,W,H)
Armor: Same as M3 GMC in-game
Ammunition: Same M3 GMC in-game
Featured in a Japanese propaganda newspaper:
Sina Visitor System
M3 Gun Motor Carriage - Wikipedia
Tank Encyclopedia - The Online Tank Museum
Half-Track: A History of American Semi-Tracked Vehicles by R.P. Hunnicutt