Beat me to it. I was just going to say it was a recoilless rifle.jmorris wrote:Well, does look like a Hummer but that's not a cannon, it's a M40 106mm Recoilless Rifle. By the late 1970s I think they'd all been transferred to the Nation Guard so I'd be surprised if an M40 106mm was ever actually mounted on a Hummer. The .50 cal is a spotting rifle. If the .50 round hits, yank the lanyard.
I remember when the Hummer H1 first became commercially available. I believe that Arnold Schwarzenegger bought the first one.