An Arty Fire Direction Control (FDC) track. In Army talk it is an M-557 Armored Carrier. Really it is an M-113 with a high ceiling and provisions for lots of radios. And if you don't fear salt water you can just drive it into the surf to wash off the sand which of course will get back on as soon as you drive ashore. Oh well, those big noises from the cannons do effect some people in strange ways.