The Priest was more of a dedicated artillery piece compared to the shortbarreled M4(105) and its M4A3 variant.
http://the.shadock.free.fr/sherman_minutia/manufacturer/m4_105mm/m4_105mm.htmlThis one still had the turret, and a dinky little sawed-off four-inch gun seemed to do pretty darn good as a mix of light field artillery and assault gun. From what I'm reading, they showed up in mid-'44 and were organized into a six-ship Assault Gun platoon for each tank battalion. They were much better at demolitions than the 75 or 76mm tanks. Good visibility, good protection, good firepower, fine mobility, but no power traverse for the turret.
Brits drove a bunch too, and apparently Free French units got their hands on a few that fell off the ship somewhere. The 105 Shermans also showed up in the Philippines and Okinawa theaters; I imagine the island fighting was probably a better fit for them with the short barrels, good armor, and high boom quotient - no need for an M4A3(76) to take out a Chi-Ha for example.
However, it should be pointed out that those were all for TANK battalions. Your granddad, God rest his soul, was in an arty BN and very definitely would have operated Priests, from what I'm reading.
https://history.army.mil/documents/ETO-OB/6AD-ETO.htmHere's the history of the 6th Armored Division, of which the 231st Armd FA BN was one of three organic arty battalions. They stayed with the division the whole time, joining a LOT of other artillery units attached from other divisions, arrived in France June 12, 1944 and made it all the way to the outskirts of Leipzig before the war ended, not very far from Berlin. At the bottom of that link there's a long list of where the division (and thus, your granddad's BN) were, so you should be able to look up histories and track down a lot more info if you're interested.
And as for the Sherman 105s, well, they got a little bit Battletech in the PTO.
That's not a dummy gun marked (1) there, that's a freakin flamethrower. AND a 105mm howitzer. I kinda want to make a Battletech version of this now, AC10 and Plasma Rifle on a tank...