AL ASAD, Iraq -- Cruising over the desert just above 400 feet, a Marine crew chief kneels behind the Gun Ammunition Unit 21 mounted on the ramp of the CH-53D Sea Stallion. The pilots and crew chiefs in the front of the aircraft relay the current target's location that will be coming into his field of fire within seconds.
A series of smoke clouds and loud pops emit from the barrel of the .50-caliber machine gun, as a succession of tracer rounds, appearing like lasers from some flashy science fiction movie, slam into the makeshift targets of old vehicles on the desert dunes.
Marine Heavy Helicopter Squadron 463, Marine Aircraft Group 16 (Reinforced), 3rd Marine Aircraft Wing, is the first CH-53D helicopter squadron to install the GAU-21 .50-caliber machine gun system onto their aircraft.
"The GAU-21 is very similar to the XM-218 .50-caliber, which is the machine gun that is mounted on the doors of the aircraft," said Cpl. Thomas D. Martinez, crew chief and weapons and tactics instructor, HMH-463. "Most people can't really tell the difference until they know a little bit about them. It is a new system to the Marine Corps. The XM-218 has been around forever, but the GAU-21 is modified to fire faster and fire slightly farther."
Purchased in January 2004, the GAU-21 is fairly new to the Marine Corps. It was first tested on CH-53E Super Stallions before moving to the aircraft's little brother, the Delta.
"It was passed on to the Deltas and tested in Hawaii," said Martinez, a 22-year-old Durango, Colo., native. "We got the clearance to fire the tail gun from the Delta platform in December last year. We chose to use the GAU-21 as the ramp system because of its ability to put more rounds down range. All we had to do was modify our ramp in order to facilitate it."
The GAU-21 was chosen over the XM-218 for its safer operability and the M-240G machine gun for the size and path of its rounds, said Cpl. Mitchell C. J. Harquail, crew chief and weapons and tactics instructor, HMH-463.
"The 7.62 round used in the M-240G is too small," said Harquail, a 26-year-old native of Sea Side, New Brunswick, Canada. "The rotor wash from the aircraft affects the rounds' trajectory. The .50-caliber is a heavier round. You need a heavy round with a higher volume."
However, between the added heat from the engines blowing through the rear of the aircraft and the added gravity from the aircraft turning or banking, this new weapon system takes a toll on the Marines who operate it.
"You get really tired when you are on that gun, as it creates a lot of fatigue," said Harquail, a graduate of Dalhousie Regional High School. "You have to shoot from the kneeling or squatting positions and hang off of the ramp of the aircraft sometimes. There is a lot more vibration and movement in the tail of the aircraft. It gets really hot back there, as well."
Although the GAU-21 can put a tremendous amount of physical stress on well-experienced crew chiefs, the importance of this weapon does not fade from their sight.
"We are normally engaged by the enemy from the rear of the aircraft," said Martinez, a Durango High School graduate. "These weapons are important because our window guns only give us coverage in less than a 180 degree angle in front. The tail gun provides 180 degrees of coverage behind and to the sides of the aircraft."
Another feature that the weapon system provides is safety, according to Harquail, who was the first designated tail gunner for the CH-53D platform with the GAU-21.
"It is more user friendly and safer," said Harquial. "The likelihood of a cook-off, which is the igniting of a round caused by the heat of an extremely hot barrel, is greatly reduced because the weapon fires from an open bolt position."
With a rate of fire almost 400 rounds per minute faster than its older brother, the XM-218, the Marines who operate this weapon cannot get enough of it.
"I love it," Harquial said. "After the initial 20 rounds go down range, the dispersion goes down a lot. The weapon has a sweet spot that once you get used to it, you can hit almost anything."