I was unaware of MOS 11C infantry mortarman.
I thought everybody in the rifle company had the rotating honor of carrying the baseplate.
They were in their own section of the weapons platoon wih three crews for their 81 mm tubes in each rifle company or a heavy mortar platoon with four 4.2" tubes at the battalion. Each section or platoon had a fire direction center when I was an 11C. That's a while ago. They've gotten new and different tubes these days. It's a little different according to the type of infantry brigade, i.e. straight leg, airmobile, airborne, mechanized and motorized. Here's a sample.