YUMA PROVING GROUND, AZ--- The C-130 Hercules cargo aircraft is a familiar sight in the skies above U.S. Army Yuma Prvoing Ground (YPG), ferrying cargo and personnel for parachute tests.
Less familiar to the workforce, however, may be the AC-130, the C-130's awesomely-armed variant, which, among other weapons, boasts a 105mm howitzer fired in combat at ground targets by a two-person crew.
As with any howitzer round, fuzes are vitally important. They not only trigger the round's detonation, but also have safety features to prevent a shell from exploding while being handled prior to firing, or from detonating too soon. There are fuzes that can be set to detonate a shell at a preset time in flight, when it detects a certain distance from the ground or a structure, when it hits a target, or after it hits a target. YPG has decades of experience testing fuzes for the Army and Marine Corps, and in some special cases for the Air Force as well.
"This is an Air Force fuze, but it is mechanically identical to one of the Army fuzes," said Steve Flores, artillery and mine branch chief. "The rounds for the Air Force are based on Army rounds, but there are some subtle differences."
Most important of these differences is the Air Force fuze's thicker shell, necessary both to keep it attached to the round and protect its intricate internal workings during a pulverizing high speed impact with a hardened target. Another key difference is the arm distance which has been increased to maintain a safe minimum functioning distance from the aircraft.
"They're trying to bust a bunker or go through the concrete wall of a fortress," said Tyler Heagney, test officer. "These fuzes are a lot heavier and designed to take the brunt of the impact so the projectile itself can penetrate easily."
"It's amazing how a fuze even survives going through something like this, and then still function," added Flores. "The fuze must survive, otherwise you're just punching a hole through the target."
Testers can't evaluate the performance of the fuze firing from an aircraft, thus it is done on the ground at YPG. Since the fuze is the item under evaluation, testers fire the rounds off of a 105mm gun tube mounted on an 8-inch howitzer's carriage to aid in the stability of the weapon platform. The stability the carriage provides means a quicker and more efficient test, as re-aiming takes less time. The fuzed rounds are shot through specially constructed targets of both plate steel and reinforced concrete. The first shot in a series is done with a spotter round prior to firing the test fuzes.
"We don't want to waste our test rounds because we only have a finite amount of them," said Heagney.
The tests have a relatively small footprint, with the rounds fired at close range as high speed cameras track every moment of a round's flight, from firing to impact, with a properly functioning fuze triggering an explosion only after the round has punched through the target. Setting up the test's steel plate targets is less time consuming than the multi-layered plywood targets used for Army fuze tests, but efficiency is always pursued with safety foremost in mind.
"Above all else we want everyone to be safe and go home at the end of the day," said Heagney. "If it takes more time, that's fine."
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