It could take a decade to build the low-yield, nuclear-tipped, sea-launched cruise missile the Trump administration called for last year, and development might not be able to start until the Pentagon finishes a next-generation, air-launched nuclear missile, a senior Pentagon official said Thursday.

In 2018, the Trump administration’s Nuclear Posture Review called on the Department of Defense and the Department of Energy — the civilian steward of U.S. nuclear warheads — to study a low-yield, nuclear-tipped, sea-launched cruise missile (SLCM) the U.S. could deploy “in the longer term.” The administration said the weapon could match and check similarly powerful Russian weapons.

But the Pentagon is already working on a next-generation air-launched cruise missile called the Long Range Standoff Weapon (LRSO), and former Navy admiral Peter Fanta, now deputy assistant secretary of defense for nuclear matters, said a similarly capable sea-launched cruise missile might tie up the infrastructure needed to create LRSO.

In considering the planned SLCM, “we are looking at the production capacity and capability of both the DoD complex and what time that missile might be available so we don’t disturb other things we are building right now,” such as LRSO, Fanta said Thursday at the ExchangeMonitor’s annual nuclear deterrence summit in Arlington, Va. 

Fanta said it takes about a decade “to build a highly sophisticated cruise missile” like LRSO. Raytheon [RTN] and Lockheed Martin [LMT] started maturing competing LRSO designs in 2017. The Air Force plans to start deploying the missile, with W80-4 warheads provided by the Department of Energy’s National Nuclear Security Administration, in the late 2020s.

“LRSO shows up some time in the late next decade,” Fanta told Defense Daily from the sidelines of the conference. “I understand how long that production time frame is, and sea launched cruise missile, we should not expect that to be any different.”

Fanta hastened to add that the low-yield sea-launched cruise missile would not necessarily be LRSO, or even an adaptation of that planned missile.

Whether the eventual low-yield SLCM bears any resemblance at all to LRSO will not be clear until after the Department of Defense and the Department of Energy complete an analysis of alternatives tentatively slated to begin in 2020. The White House had not released a formal 2020 budget request at deadline Thursday, but the Department of Energy in November said it would support the Pentagon’s analysis of alternatives for the low-yield SLCM in 2020.

Fanta would not say exactly when work could start on the low-yield SLCM. He also would not say which Department of Energy-provided warhead would be available to tip the missile. However, he is confident a nuclear warhead will be available by the time the future SLCM is ready for one.

“[I]f you realistically align when the next cruise missile of that capability would be available to be built, we have pretty much determined that there is an availability of [Department of Energy] infrastructure to produce the weapon that would be associated with it,” Fanta said.