Status Report: Char D1 82mm SPG
In October 1929, the Char D1 medium tank was accepted to service in the French army. It was an advanced (further developed) version of the Renault NC light tank (which in turn was a development of the venerable Renault FT). In its time, there were many projects of self-propelled guns on Renault FT chassis and the D1 (factory designation Renault TY) was to share this fate of becoming a plaform for various other projects.
In 1930 a project was proposed to arm the Renault TY chassis with some sort of 82mm gun. What gun exactly that was is not known, but such caliber was not used by the French army normally.
The chassis itself was not changed much and the gun was mounted facing to the rear of the vehicle. This allowed the chassis to carry a much bigger gun than it usually could and it wasn't really that big a problem tactically - the vehicle was supposed to be firing from dug-in positions anyway with the driver not being present inside the hull at the same time.
Compared to the D1 itself, the vehicle was 2 tons lighter (the weight was reduced from 14 tons to 12 tons), which meant that the mobility didn't suffer. The crew consisted of 5 men with the driver not sitting inside when the vehicle was supposed to fire. It was proposed that this vehicle would be a part of the Maginot line defenses along with the Char BB project. Units of these vehicles would operatively move around the line to help repel the attackers wherever needed, supporting the line defenses with their fire.
This project was not as outlandish as the Char BB but its fate was sealed nevertheless during the same disarmament conference and it was cancelled in 1932. The design however is completely realistic and the "let's build a SPG on Char D chassis" idea returned two years later with Char D2, but that was a completely different vehicle.