The U.S. Missile Defense Agency (MDA) isn’t testing its most powerful missile-interceptor enough, the Government Accountability Office claimed in a June 2019 report. The military bumped back one key trial multiple times over a period of 13 years.

Equally troubling, many of the tests the MDA is conducting aren’t very realistic, the watchdog agency explained in its report. Laura Grego, a missile-defense expert with the Union of Concerned Scientists in Massachusetts, called the GAO report “remarkable.”

The GAO focused its attention on the Flight Test Ground-Based Interceptor 11 test, or FTG-11. That test, which took place in March 2019, involved a salvo of two Ground-Based Midcourse Defense missiles (GMD), which the United States has deployed in order to destroy nuclear-armed Intercontinental Ballistic Missiles heading for North America.

The MDA attempted its first trial interception with the GMD system in 1999.

Twenty years later on March 25, 2019, the target rocket in FTG-11 blasted off from the Reagan Test Site on Kwajalein Atoll in the Pacific Ocean. Space, ground- and sea-based sensors tracked the target. Four thousand miles away, missileers at the GMD site at Vandenberg Air Force Base in California launched two 50-feet-tall Ground-Based Intercept missiles.

Kill vehicles separated -- in essence, non-exploding warheads -- separated from the GMI missiles and broke free of Earth's atmosphere. There at the edge of space, the kill vehicles reportedly met the incoming target rocket.

"This test was the first salvo engagement of a threat-representative ICBM target by two Ground Based Interceptors, which were designated GBI-Lead, and GBI-Trail for the test," the Missile Defense Agency stated.

“The GBI-Lead destroyed the reentry vehicle, as it was designed to do. The GBI-Trail then looked at the resulting debris and remaining objects, and, not finding any other reentry vehicles, selected the next 'most lethal object' it could identify and struck that, precisely as it was designed to do."

"This was the first GBI salvo intercept of a complex, threat-representative ICBM target, and it was a critical milestone," MDA director Samuel Greaves stated. "The system worked exactly as it was designed to do, and the results of this test provide evidence of the practicable use of the salvo doctrine within missile defense."

But the success came with caveats. As the GAO pointed out, the MDA originally hoped to conduct FTG-11 in 2006 in order to test the GMD system’s ability to target a single ICBM with more than one interceptor, a redundancy measure to ensure the ICBM’s destruction.

But the agency repeatedly delayed FTG-11 as it discovered more and more problems with the GBD. “MDA initially planned to conduct the salvo test in fiscal year 2006 but subsequent test failures, developmental challenges and fielding priorities delayed the salvo test to fiscal year 2018,” the GAO reported.

“FTG-11 was further delayed from the end of fiscal year 2018 to mid-fiscal year 2019 to accommodate other [Ballistic Missile-Defense System] testing priorities while GMD fixed software issues uncovered during pre-test planning.”

By mid-2017, GMD began experiencing delays developing a software upgrade that is intended to provide the kill vehicle with the functionality needed for FTG-11. Around that same time, MDA also realized that its BMDS-level integrated test schedule could not be executed as planned due to a lack of test range and asset availability.

According to a May 2018 report MDA submitted to Congress, the agency delayed FTG-11 from the fourth quarter of fiscal year 2018 to the second quarter of fiscal year 2019 to de-conflict the integrated test schedule.

Around the time MDA submitted the report to Congress, the GMD program also uncovered performance concerns with the kill vehicle software upgrade that further delayed the software’s completion. As such, the delay to FTG-11 to accommodate other BMDS testing priorities also afforded MDA the time necessary to complete the software improvements and pre-test planning.

The performance issues MDA uncovered in pre-test planning for FTG-11 demonstrate the value of rigorous and frequent GMD testing. Congress and [the U.S. Defense Department] have recognized the need for rigorous, operationally realistic GMD testing, including conducting a salvo test. Congress also passed legislation and the president signed into law a requirement for an annual GMD flight test, subject to several exceptions.

However, GMD has historically averaged less than one test per year whereas Aegis Ballistic Missile Defense Standard Missile-3 averaged over 2.5 tests per year.

The delays and the slow pace of testing, which as FTG-11 proved can result in further delays, aren’t the GMD’s only problems, the GAO explained. “GMD’s prior tests achieved less than 50-percent operational realism whereas Aegis BMD SM-3 averaged over 70 percent, according to Director for Operational Test and Evaluation assessments.”

“The warfighter relies on testing to understand GMD’s capabilities and limitations. Without this knowledge, the warfighter lacks the information to operate GMD effectively and efficiently.”

David Axe serves as Defense Editor of the National Interest. He is the author of the graphic novels  War Fix, War Is Boring and Machete Squad.