STORY: :: FileThe U.S. Air Force's B-2 stealth bomber played a key role in strikes against Iran's nuclear sites on Saturday.The U.S. military said seven of the bombers were used in "Operation Midnight Hammer”...:: Whiteman Air Force Base...to fly for 18 hours from an air force base in Missouri to Iran to drop precision-guided munitions on three nuclear sites.The cutting-edge design of the B-2 includes features that make it stealthy, and reduce infrared, radar and acoustic signatures.But the flying wing’s success ultimately hinges on human performance, and intercontinental, multi-day flights demand extraordinary endurance from its two-person crew.Diet is carefully considered, and pilots go through sleep studies in advance of missions to see what wakes them up and helps them sleep.Reuters spoke with one retired B-2 pilot who said his go-to meal for the multi-day flights was turkey sandwiches, without cheese.The blander the better, he said.Some pilots also sneak in sunflower seeds to stay alert between meals.The B-2's cockpit includes a small area behind the seats, where pilots can lie down on a cot.While the B-2 can fly 6,000 nautical miles on a full tank, most missions require multiple mid-air refuelings.It’s one of the most dangerous aspects of these missions.Refueling is done blind.Pilots can't see the boom extending from a tanker full of gas attaching to the B-2 16 feet behind their heads.Instead, they rely on visual cues from the tanker's lights and memorized reference points.While updates to the B-2's software since its 1989 debut have improved responsiveness to pilot commands, flying in tight formation at high altitude remains a challenge.And the process becomes increasingly difficult as pilot fatigue sets in.The B-2 costs about $65,000 per hour to operate.Over the coming decades, the Air Force says it plans to replace the B-2 and B-1 fleets with at least 100 B-21 Raiders.