The operation was set for Saturday, but had to be postponed a day due to weather. At 1:30 a.m. on Monday morning in Pakistan time, two helicopters carried about 25 SEALs to the compound with a second team as backup. Meanwhile, back in Washington, Mr. Obama and his national security team watched live on television monitors as the operation unfolded.

"It was probably one of the most anxiety-filled periods of time, I think, in the lives of the people who were assembled here yesterday," Brennan said.

Adding to the tension was the fact that Pakistani military officials scrambled air force jets in response to the situation, which they had no prior knowledge of. However, the U.S. forces were able to exit Pakistan's air space without incident, Brennan said.

The operation's helicopters -- reportedly a HH-60 "Pave Hawk" and a CH-47 -- came under fire from security forces firing from the roof of the compound. The Pave Hawk had mechanical failure and made a hard landing after half the platoon "fast roped" into the compound. At least two other helicopters were part of the initial assault. When the Pave Hawk couldn't get back in the air, it was destroyed to protect the ship's sensitive avionics and communication equipment.

"When that helicopter was seen to be unable to move, all of a sudden you had to go into Plan B," said Brennan.

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