About 4,700 active and reserve soldiers are on the U.S. border with Mexico in support of President Trump’s efforts to stem illegal immigration, but according to Army senior leaders, the unexpected mobilization late last year hasn’t impacted the service’s overall readiness.

While the deployed units did have to drop their plans to head south, the effect is small, Army Secretary Mark Esper and Army Chief of Staff Gen. Mark Milley told Sen. Martin Heinrich, D-N.M., during Senate Armed Services Committee testimony on Tuesday.

“In the scale of a 1.1 million-man Army, the impacts on readiness, if there are any, are negligible,” Esper said. “It’s part of our mission set that we accept.”

The effort is comparable to many of the Army’s impromptu humanitarian aid missions, Milley added.

“Any time an Army unit goes on an unplanned contingency op, whether it’s Hurricane Katrina or Puerto Rico or Ebola, or goes to Afghanistan or wherever ― doesn’t matter where it is ― they’re going to cancel whatever they were doing prior,” he said. “So the short answer would be yes, for the specific units.”

Heinrich’s question was inspired by a March 18 letter, first made public by the Los Angeles Times, from Marine Corps commandant Gen. Joseph Neller, requesting funding relief from Navy Secretary Richard Spencer, in light of the impact border deployments would have on several of the Corps’ planned exercises.

For the Army, Milley said, the deployments don’t cut nearly as much into readiness.

“The larger answer, though — does it impact the readiness of the Army? And the answer is: No, it doesn’t have a significant impact at all,” he said. “It’s a very modest, negligible impact on the Army as a whole, primarily because of scale, which is a slightly different scale than what the Marines are talking about in that letter.”

Most of the deployed soldiers are support personnel, he added.

“So our assessment is that the units that are going down there — primarily engineers, [military police], some aviation, transportation, medical units ― they’re within their mission profile, in terms of the tasks that they’re actually doing,” he said.

After an initial deployment last fall, the Pentagon announced in January that troops would continue to support border security until September.

At Heinrich’s request, Esper agreed to provide SASC a list of Army exercises that have been impacted by soldiers deploying to the border.