By Mike Stone

WASHINGTON (Reuters) -Before strapping into the cockpit of the U.S. Air Force's B-2 Spirit stealth bomber for missions that can stretch beyond 40 hours, pilots undergo weeks of preparation that focuses not only on flight plans, but what to eat.

The B-2, a $2 billion flying wing built by Northrop Grumman, played a key role in delivering strikes on Iran's nuclear sites on Saturday. It demands extraordinary endurance from its two-person crew. That starts with understanding how nutrition affects alertness and digestion during intercontinental flights that can span nearly two full days.

"We go through sleep studies, we actually go through nutritional education to be able to teach each one of us: one, what wakes us up and then what helps us go to sleep," said retired Lt. Gen. Steve Basham, who flew the B-2 for nine years and retired in 2024 as deputy commander of U.S. European Command.

Pilots are trained to be cognizant of foods and how they slow or speed digestion - critical in an aircraft with a single chemical toilet. Basham's go-to meal: turkey sandwiches on wheat bread, no cheese. "As bland as you possibly can," he said.

With a 172-foot (52.4 m) wingspan and stealth profile, the B-2 can fly 6,000 nautical miles without refueling, but most missions require multiple mid-air refuelings. That process becomes increasingly difficult as fatigue sets in.

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. At night, especially on moonless flights, the task becomes what Basham called "inherently dangerous."

"Adrenaline kept you going before you went into country," he said. "The adrenaline goes away. You try to get a little bit of rest and you still got that one last refueling."

The B-2's cockpit includes a small area behind the seats, where pilots can lie down on a cot. Sunflower seeds help some stay alert between meals.

Despite its cutting-edge design - features that make it stealthy reduce infrared, radar and acoustic signatures - the B-2's success hinges on human performance. The aircraft's two-person crew replaces the larger teams required for older bombers like the B-1B and B-52, placing more responsibility on each member of the flight crew.

The B-2's fly-by-wire system, which relies entirely on computer inputs, has evolved since its 1989 debut. Early software lagged behind pilot commands, complicating refueling, Basham said. Updates have improved responsiveness, but the challenge of flying in tight formation at high altitude remains.

During Operation Allied Force in 1999, B-2s flew 31-hour round trips from Missouri to Kosovo, striking 33% of targets in the first eight weeks, according to the Air Force. In Iraq, the aircraft dropped more than 1.5 million pounds of munitions across 49 sorties.

The Air Force plans to replace the B-2 and B-1 fleets with at least 100 B-21 Raiders over the coming decades. The B-2 costs about $65,000 per hour to operate, compared to $60,000 for the B-1, Pentagon data shows.

"Our pilots make it look easy, but it's far from easy," Basham said. The B-2's complicated missions can't be done "without a massive, massive array of planners on the ground throughout the world and maintainers that make sure you've always got a good aircraft."

(Reporting by Mike Stone in Washington; Editing by Stephen Coates)