U.S. troops in Iraq are firing .50-caliber machine guns at such a high rate, the Army is scrambling to resupply them with ammunition - in some cases dusting off crates of World War II machine gun rounds and shipping them off to combat units.

Small wonder, then, that the steady increase in .50-cal use began to drain ammo stockpiles rapidly. At the Blue Grass Army Depot in Richmond, Ky., ammunition left over from Desert Storm, Vietnam, Korea and even World War II had been stored in massive concrete bunkers, including some 12 million rounds of .50-cal.

"Fifty-cal is crazy," said Bryce Hallowell, spokesman for Alliant Techsystems Inc., the contractor that runs the plant. Four years ago, Lake City was manufacturing about 10 million rounds a year; currently it is producing at an annual rate of 50 million rounds and rising.

Even that fivefold increase hasn't been enough.

At Blue Grass, Darryl Brewer, a combat medic in Vietnam, is chief of logistics for the ammunition depot. Recently, he started pulling out .50 cal. crates marked 1945.

Fifty-cal rounds are linked into belts that are fed from steel ammo boxes into the side of the weapon. At Blue Grass, technicians have to replace the World War II links, using a "delinker- linker" machine so old they had to make parts for it before it would work. The relinked rounds are sealed back in ammo boxes, like sardines, and shipped.