In January, the Reuben James took one for the team. Parked off the coast of Hawaii one moment, the decommissioned U.S. Navy frigate was struck by a supersonic Standard Missile-6 missile the next, sending the Reuben James to the bottom of the ocean. By all meaningful measures, it was a successful test of an anti-ship missile.

But the SM-6 isn’t an anti-ship missile—or at least it wasn’t designed as one.

The Standard Missile-6, built by Raytheon rtn and carried by U.S. Navy destroyers and cruisers around the globe, is a defensive weapon designed chiefly to defend those ships and the aircraft carriers they accompany from incoming attack aircraft and missiles. That test, the details of which were made public this week, marks the first time an SM-6 air defense interceptor has destroyed a surface target at sea.

It also marks a significant milestone in the Navy’s efforts to develop something it calls “distributed lethality,” or the ability to strike at naval targets from any ship at any location at any time. Facing new threats at sea, the Navy wants to make its adversaries (read: China) worry about every ship in the fleet as a lethal threat, not just the aircraft carriers that are the Navy’s crown jewels.

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Just as significantly, the test also marks the latest move in a Pentagon effort to push existing weapons to do more with a minimum of re-engineering or upgrading.

That effort is borne both of budget constraints and concerns about new threats at sea for which U.S. Navy hasn’t had to prepare since the end of the Cold War. In the years since then, the Navy has placed its money and its focus on weapons that can strike targets on land and actively defend its aircraft carriers (which can themselves launch aircraft to strike targets on land and at sea) from airborne threats. Destroyers and cruisers are now typically loaded down with a complement of SM-6 air defense missiles and Tomahawk land attack cruise missiles, creating something of a capability shortfall where ship-to-ship combat is concerned.

That shortfall has become a liability particularly as China continues to expand its maritime warfare capabilities both by growing its navy and increasing its military presence in the South China Sea. As a result, the SM-6 isn’t the only U.S. naval asset getting an expanded mission profile.

In February 2015, a U.S. Navy ship-based Tomahawk missile—originally designed to strike targets on land—punched a hole in a moving barge, demonstrating that system’s ability to carry out ship-to-ship warfare as well. The current Pentagon budget request sets aside $484 to convert a portion of the Navy’s stores of Tomahawk missiles into ship-killing cruise missiles that can strike targets at ranges up to 1,000 miles.

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Raytheon has already delivered some 250 SM-6 missiles to the U.S. Navy, which first deployed them in 2013. The Pentagon’s five-year budget has earmarked another $2.9 billion for 625 more of the missiles, Secretary of Defense Ash Carter said in February.

In tests separate from the one that sunk the Reuben James, SM-6 missiles recently destroyed five targets in “over-the-horizon” tests in which the missiles relied on their own onboard radar—rather than targeting information provided by the launching ship—to track and destroy targets in flight. It was the longest range test of the SM-6, to date.

While the SM-6 doesn’t have the same kind of range as the subsonic Tomahawk, its supersonic speed makes it tougher for adversaries to shoot down, giving existing U.S. naval ships two complementary and effective ship-killing options.

Critically, the Navy didn’t have to fund and develop an entirely new surface warfare missile that ships would then have to make room for at the expense of their air defense interceptors and land attack cruise missiles.