During debate Tuesday on the fiscal 2017 defense authorization bill, the Senate adopted an amendment aimed at forcing the Pentagon to address a security shortfall at U.S. nuclear missile sites.

The Senate adopted by unanimous consent a package of 16 amendments to the bill (S 2943), including one by Montana Republican Steve Daines that would trigger a Defense Department review of nuclear missile security.

Some 450 of America’s intercontinental ballistic missiles, or ICBMs, are scattered across hundreds of miles near three Air Force bases in Montana, North Dakota and Wyoming. The security force protecting those far-flung installations has relied for years on nearly three dozen Vietnam-era UH-1N Huey helicopters. But CQ disclosed in February that a classified exercise last summer revealed that the aging Hueys were no longer capable of adequately responding in case of an attack on a missile site.

Congress has swung into action to address the problem. Daines’ amendment would require the secretary of Defense and chairman of the Joint Chiefs of Staff to decide if a security shortfall exists and tell Congress within 30 days of the authorization law’s enactment whether additional forces are needed at the ICBM bases. If the answer is “yes,” the secretary must either implement the changes within 60 days or tell Congress when the department will do so.

The amendment varies from a provision Daines was able to secure last month in the Senate Appropriations Committee’s Pentagon spending bill (S 3000). That language would direct the chief of U.S. Strategic Command to give Congress a classified report that describes the threat that has arisen because of the aging Hueys, the number of helicopters needed for the job and their capabilities, and the risks involved with shortfalls that have been identified.

In the meantime, the Pentagon must get aircraft to the missile fields promptly to address the potential risks, the spending bill says. And the Defense secretary must confirm to Congress 180 days after the fiscal 2017 spending law is enacted that the ICBM security problem has been solved.

A number of lawmakers concerned about ICBM security would like to see the Air Force procure as many HH-60 Blackhawks as necessary and do it as soon as possible.

The Pentagon, however, has said that a competition should occur to select a new helicopter. Many lawmakers who represent helicopter manufacturers would like their companies to vie for that award, which could be valued at more than $1 billion.

In the meantime, Deputy Defense Secretary Robert Work told senators last month the Pentagon  is considering nearer-term options for moving aircraft from other locations to shore up security at the ICBM facilities.

So far, Congress has not clarified whether it would prefer a competition or not. Only the Senate’s defense authorization bill is clear on this. It would approve $321 million to replace the Hueys, and the measure specifies that the money should be spent on eight Blackhawks.

The House Armed Services bill (HR 4909) would authorize $80 million to address an “urgent need,” but the measure doesn’t spell out what should be bought.

The Senate Appropriations Defense spending bill contains $75 million for the initiative and also does not direct how the funds should be spent.

The House Appropriations Defense bill appears to be silent on the issue.