WASHINGTON — There's growing concern the U.S. Army's munition stockpile is shrinking as it supports operations in the Middle East, and Rep. Bill Shuster, R-Pa., is pushing to prevent the service's lower-cost interceptor — the Patriot Guided Enhanced Missile — from being phased out of the inventory.

Aside from the U.S. Army, the GEM-T — used to intercept tactical ballistic missiles — is in the inventory of five countries where all except one are in the Middle East and are likely being used to intercept tactical ballistic missile launches by Houthi militants in Yemen.

The Saudi Arabian government most recently reported intercepting four tactical ballistic missiles fired by the rebel force at the end of March, just another attack in a long string of attacks.

"Since Jan. 1, 2015, Patriot has intercepted more than 100 Tactical Ballistic Missiles during combat operations; more than 90 of those 100+ intercepts were with the GEM-T," read a letter from Shuster, which was circulated to House colleagues last month.

But while tactical ballistic missile attacks heat up in the Middle East signaling a greater need, the Army made a decision not to recertify the GEM-T missile several years ago and it now stands to be slowly phased out of the inventory.

The decision not to recertify the GEM-T seems to have been based strictly on budget woes the Army faced in 2013 under the Budget Control Act, according to a senior Capitol Hill defense staffer.

In a perfect world, the Army would have funded both the recertification of the GEM-T missile and the production of its most state-of-the-art Patriot missile — the Missile Segment Enhanced version. But with depleting funds, the Army had to prioritize Patriot MSE, the staffer said.

Indications from the Army is it wants to have GEM-T in the toolkit should funding become available, the staffer added.

The Army’s decision has now led to a couple of problems. The service is headed toward an inventory issue, for one. Ten years from now, as systems reach the recertification timeline, they will be taken out of the inventory and demilitarized instead. At the same time, MSE missiles are not being produced at a rate of one-for-one to replace GEM-Ts as they are taken out of service.

Therefore the inventory levels are going to creep lower and lower to a point where there’s not enough in the Army’s stockpile to safely meet the threats GEM-T is designed to defeat, according to the staffer.

The Army will also have to turn more and more to deploying MSE missiles for jobs against threats the GEM-T was meant to take out, essentially using a missile roughly twice the cost of GEM-T for targets that don’t require that level of capability.

It’s estimated the cost to recertify the GEM-T missile is roughly 5 percent of the cost of a PAC-3 MSE that has a price tag of roughly $5 million. A new GEM-T would cost roughly 50 percent less.

Shuster is introducing his stand-alone bill to look at preserving the GEM-T missile at a time when the budget environment is set to change, possibly with increased defense funding. And the growing concern over munitions stockpile shortages could serve as an impetus to keep capable and low-cost interceptors around longer.

The bill "would avert a potential missile defense crisis within the Army and would have the potential to save American taxpayers millions of dollars," Shuster said in a statement provided to Defense News.

The bill would not allow funds to demilitarize GEM-T interceptors until after the Army delivers an evaluation of its ability to meet its requirements and operational needs if GEM-Ts were taken out of the inventory.

The legislation instructs the Army chief of staff and secretary to evaluate whether the service can maintain an inventory of interceptors that retain GEM-T capability either through recertifying the interceptors with or without modification or upgrades or by developing, testing and fielding a new, low-cost interceptor that can be placed in the service’s inventory before the retirement of GEM-Ts.

Letterkenny, the Army’s primary missile depot, is in Shuster’s district. The majority of Patriot interceptors come through Letterkenny.