A Retrograde Wheelbarrow is where the female places her hands on the ground to support herself whilst the male picks up her lower body and thrusts into her, mimicking a wheelbarrow (with extra sex).
A Retrograde Machinegun Wheelbarrow is the same, but the female places her hands onto a machine gun emplacement and fires, causing vibrations to resonate throughout the female, and into the male, resulting in increased pleasure for both members.
May be performed during actual defence of a position for extra tension.
The Soviet Army 1939-1945
I'm pretty damn sure the Retrograde Machinegun Wheelbarrow (or "Machine Gun Fucking") occurred then.