An Air Force unit that operates one-third of the nation’s land-based nuclear missile force has failed a safety and security inspection, marking the second major setback this year for the force, the general in charge of the Air Force’s nuclear force told The Associated Press on Tuesday.

According to an AP article, the failure was recorded by the 341st Missile Wing at Malmstrom Air Force Base, Mont., which is responsible for 150 Minuteman 3 nuclear missiles that stand on 24/7 alert for potential launch against targets around the globe. According to Lt. Gen. James M. Kowalski, the 341st wing failed a “small team exercise” as part of a broader inspection, which means that the whole inspection was a failure.

 The general said this did not call into question the unit’s safe operation of nuclear missiles but was its second safety and security inspection failure in just over three years.

While details of the failure or the exerciser remain under wraps, Kowalski said that it did involve the crews who monitor the missiles from inside underground launch control capsules, and a written statement said that there had been “tactical-level errors” during the exercise, revealing “discrepancies,” the article reports.

Those who failed the exercise will be retested within three months.