Their plan called for the military to draw down to zero within 60 days of Biden’s official order, or roughly mid- to late-June — far sooner than the Sept. 11 deadline the president originally set. One of the most crucial decisions involved handing over Bagram Air Base to the Afghans as the last step of the withdrawal once U.S. forces were so depleted that they could no longer reasonably secure what had been the hub of the American military effort there for the past 20 years.

“All of them made the same argument,” said one defense official, who was in attendance at the drill on May 8, and whose account includes previously unreported details. “Speed equals safety,” the person said, referring to the message conveyed by the military leaders.

The military brass had done a remarkable 180. For the first four months of 2020, as the White House reviewed the withdrawal timeline inherited from the Trump administration, Austin and Milley, as well as senior military commanders, urged Biden to leave a few thousand troops in Afghanistan indefinitely. Both were overruled. Once that happened, the Pentagon embraced as quick a withdrawal as possible, including from Bagram. And the Pentagon stuck to that approach through the beginning of July, regardless of the conditions on the ground.