The U.S. Air Force moved forward Wednesday with a program to extend the U.S. arsenal of nuclear-capable missiles, when it awarded Lockheed Martin and Raytheon separate $900 million contracts to start work on a cruise missile that is meant to be fired from a B-52 or B-2 bomber.

The missile, called the Long Range Standoff weapon, is to replace the aging AGM-86B cruise missile, an older weapons system that was built by Boeing.

“This weapon will modernize the air-based leg of the nuclear triad,” Air Force Secretary Heather Wilson said in a statement. “Deterrence works if our adversaries know that we can hold at risk things they value. This weapon will enhance our ability to do so, and we must modernize it cost-effectively.”

Each company will have an estimated 4½ years to develop an updated version of the missile before a single company is selected to manage the program.

The United States is in the process of drawing down its stock of nuclear warheads under the terms of international nonproliferation agreements. In the meantime the Pentagon is working to update its capability to quickly and accurately deliver those weapons should the need ever arise.

Some see the missile as destabilizing and unnecessary. Sen. Dianne Feinstein (D-Calif.) pressed Defense Secretary Jim Mattis on the issue during an appropriations hearing.

“It’s got features which concern me greatly,” Feinstein said. “I don’t see it as an effective deterrent weapon. I see Russia taking action to counter it.”

The award comes just days after the Air Force moved to reoutfit the Pentagon’s ground-based ballistic missiles, when it issued two development contracts for a missile called the ground-based strategic deterrent.

Both are meant to update the country’s ability to quickly deliver nuclear weapons, a set of capabilities that officials admit is badly in need of repair.