I vaguely remember seeing this when I was a kid.
It was either a tank, car, or aircraft, but basically you drove it like a normal vehicle with your hands, but the “pedals” were actually what activated the guns. In order to shoot you hit the right pedal with your feet and it would fire once with every step on the pedal. I forgot if it was semi-automatic or fully auto. The left pedal I believe was a manual eject if you had a jam.
Some WW2 era tanks used a pedal for firing the main gun, hands were used for aiming.
I believe the M4 Sherman used pedals in at least some variants.
I was a Gun Fire Control tech on the USS Virginia CGN-38.
We had a Mk86 gun fire control system the directed two 5" 54 cal gun mounts… It was fired with a foot peddle from the CIC (combat information center).
When we were evacuating Lebanon in 82ish maybe 83 we fired countless rounds into the hills behind Beirut. I personally probably fired 50-75 rounds.
September 1983. The nuclear-powered missile cruiser USS Virginia, and the destroyer USS John Rodgers, the frigate USS Bowen, and the destroyer USS Arthur W. Radford fired 338 rounds from their five-inch (127 mm) naval guns in support of the Lebanese Army units defending Souk El Gharb. Eventually, the Lebanese Army’s Eighth Brigade bore the brunt of the attacks, but succeeded in retaining control of the town after three days of heavy fighting. However, it remains an open question whether they would have held it without the American naval support
Isn’t there a very brief shot of that in Kelly’s Heroes? I seem to recall that but I could be wrong.
The widely used Bofors 40mm anti-aircraft gun is fired using a foot pedal. The vehicle mounted version was what Ned Beaty was shooting in the movie 1941.
I don’t know about Kelly’s Heroes but certainly this is shown in Fury:
Around 2.20
Here’s an instructional video. 
They definitely showed that in Fury - several shots, the camera goes to Shia leBoeuf’s foot stomping down on a floor pedal.