A warning siren bellowed through the concrete bunker of a top-secret Naval facility where U.S. military engineers prepared to demonstrate a weapon for which there is little defense.

Officials huddled at a video screen for a first look at a deadly new supergun that can fire a 25-pound projectile through seven steel plates and leave a 5-inch hole.

The weapon is called a railgun and requires neither gunpowder nor explosive. It is powered by electromagnetic rails that accelerate a hardened projectile to staggering velocity—a battlefield meteorite with the power to one day transform military strategy, say supporters, and keep the U.S. ahead of advancing Russian and Chinese weaponry.

In conventional guns, a bullet loses velocity from the moment the gunpowder ignites and sends it flying. The railgun projectile instead gains speed as it travels the length of a 32-foot barrel, exiting the muzzle at 4,500 miles an hour, or more than a mile a second.

“This is going to change the way we fight,” said U.S. Navy Adm. Mat Winter, the head of the Office of Naval Research.

The Navy developed the railgun as a potent offensive weapon to blow holes in enemy ships, destroy tanks and level terrorist camps. The weapon system has the attention of top Pentagon officials also interested in its potential to knock enemy missiles out of the sky more inexpensively and in greater numbers than current missile-defense systems—perhaps within a decade.

The future challenge for the U.S. military, in broad terms, is maintaining a global reach with declining numbers of Navy ships and land forces. Growing expenses and fixed budgets make it more difficult to maintain large forces in the right places to deter aggression.

“I can’t conceive of a future where we would replicate Cold War forces in Europe,” said Deputy Secretary of Defense Robert Work, one of the weapon’s chief boosters. “But I could conceive of a set of railguns that would be inexpensive but would have enormous deterrent value. They would have value against airplanes, missiles, tanks, almost anything.”

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