The Black Hawk helicopter that collided with a passenger jet in Washington on Wednesday was on a training flight along a route core to a seldom-discussed military mission to evacuate senior officials to safety in the event of an attack on the U.S., officials say.

The Black Hawk military helicopter involved in Wednesday’s midair collision was training to evacuate government officials in the case of a catastrophic event when it crashed into an American Airlines regional passenger plane – creating a catastrophe of its own.