This is a Japanese Type 41 75mm gun. This particular mountain gun wreaked havoc on the 1st Marines during the Peleliu landing. It was located atop a ridge and concealed in a cave. On D-plus 2, the gun rolled out and fired on a machine gun squad supporting the 1st Marines. The MG squad was wiped out but the action caught the attention of a nearby tank and, in cooperation with a bazooka man, destroyed the gun. Here's a before & after shot of that gun.