MH-53J Pave Low III

US Air Force (USAF) MH-53J Pavelow III helicopter takes off on a night mission in support of Operation Enduring Freedom, Feb 2003. Note the crew chief standing on the partially-opened rear ramp. It's not uncommon for a .50 cal machine gun to be fitted pointing out of the open the rear ramp. Like with the 2 side gun ports, the rear gun is used to keep the heads down of any enemy troops both along the route and around the insertion/extraction point.