The U.S. Air Force has reiterated its intention to begin developing a new long-range stand off (LRSO) nuclear missile later this year to equip its strategic bomber fleet. The service plans to field the LRSO in 2030 to replace the current, Boeing-built AGM-86B air-launched cruise missile (ALCM) that originally entered service in the 1980s.

On January 21, the Air Force announced that it had recently tested the capability of the B-52H Stratofortress to deliver three unarmed ALCMs, and it reconfirmed plans to award potentially two preliminary design contracts for the LRSO in the fourth quarter of Fiscal Year 2017—the months of July through September.

The FY2017 defense authorization act that former President Barack Obama signed into law in December allocated $95.6 million to advance the LRSO development. But President Donald Trump’s new defense secretary, retired Marine Gen. James Mattis, has not yet pledged his support of the program, which will cost an estimated $20 billion or more for some 1,000 missiles.

“I need to look at that one, sir,” Mattis said, when asked about the LRSO during his confirmation hearing before the Senate Armed Services Committee on January 12. “My going-in position would be it makes sense, but I need to look at it in terms of deterrent capability.”

The Air Force has said the LRSO is critical to recapitalizing the air component of the U.S. nuclear triad, which depends on gravity bombs and the ALCM—its lone nuclear cruise missile. The service plans to fit the new missile on the B-52H, the stealthy B-2 Spirit and the future B-21 Raider. “Nuclear-capable bombers armed with standoff missiles provide the nuclear triad a clear, visible and tailorable deterrent effect, and deny geographic sanctuaries to any potential adversary,” the service says.

On July 29 last year, the Air Force released a request for proposals to industry for the LRSO technology maturation and risk reduction phase. Boeing, Raytheon, Northrop Grumman and Lockheed Martin have been reported to be vying for the risk-reduction phase. The service plans to award up to two contracts; the winners will then have four and a half years to complete a preliminary design “with demonstrated reliability and manufacturability,” after which the Air Force will select one contractor to build the missile.