I have a similiar photo of my son carrying an M4 (I think they had to carry them everywhere), only his M240 was mounted on the loader's hatch on a tank. Since he was a tanker, they originally all had pistols but they turned them in sometime during their deployment. I guess they figured they were useless or something.
You may also recall the army's designated marksman program, which included liberal distribution of such goodies as .50 caliber rifles. Even tank units received them but again, they apparently thought they were useless in their role and I can understand why. The army definately has no weapon shortages. Some units even deployed with weapons that were never taken out of the shipping containers.
Shoot low, sheriff. They're riding Shetlands!
Underneath the starry flag, civilize 'em with a Krag,
and return us to our own beloved homes!
Buy War Bonds.