I see photos of M4A3 Sherman's from WWII with an additional piece of armor plate welded on the side where the drivers station is.
Was this a factory modification of something done in the field?
Steve

Done in the field.... the factory “ up armor” Sherman was called the jumbo... m4a3e2.... search “jumbo Sherman “ on the inter webs...

+1,that's a field mod. You can tell it from the Jumbo because the latter has a more uniformous protection scheme, with heavier armor covering the entirety of the front and sides of the hull. If you see plates of steel "stuck" to the side of the tank, it's more or less jerry rigged, although it beats stacking sandbags on the vehicle!

If it is some small armor plates, about 3 feet square, then it's a factory made, but often field installed extra armor to cover the area where the sponson ammo storage was. They also added a welded on armor plate to the turret on the gunners side to cover a thin spot in the casting. When they changed over to wet ammo storage in the floor, those add on armor plates were not needed any more.