The U.S. attack on Iran’s nuclear sites was a complex mission that used decoy bombers and “misdirection” to carry out the secret operation, Defense Secretary Pete Hegseth said at a news conference Sunday morning.

Joint Chiefs of Staff Chairman Gen. Dan Caine, standing with Hegseth, said the mission was a “complex and high-risk mission” that was known to only a few people and relied on decoys to protect the integrity of the mission.

Decoy B-2 stealth bombers flew over the Pacific toward Guam on Saturday to draw attention away from the mission, Caine said. News reports at the time reflected the movements.

But the B-2 stealth bombers actually used in the mission were deployed earlier and flew under the cover of darkness for 18 hours to reach their destination on Saturday evening, Caine said.

The B-2s flew nonstop, refueling multiple times in flight in what became the longest flight involving the fleet since 2001, he added.

“It took a great deal of precision. It involved misdirection and the highest of operational security,” Hegseth said, adding that the B-2s went “in and out and back without the world knowing at all.”

A total of 14 bunker buster bombs were dropped — with the first two dropped at 2 a.m., Iran time. The attack also involved a U.S. submarine that launched more than two dozen Tomahawk land attack cruise missiles at key surface targets.

“Throughout the mission, we maintained the element of surprise,” Caine said.

Iran did not deploy fighters or surface to air missiles during the mission, Caine said — a signal that Iran was caught off guard by the attack as well.

ABC News’ Anne Flaherty and Luis Martinez contributed to this report.