B-47 Pilot Recalls Flying Largest Nuclear Bomb from UK to Spain

Stratojet crew faced unique challenges transporting massive Mark 36 hydrogen bomb

Jan. 30, 2026 at 8:15am

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In the summer of 1959, a B-47 Stratojet crew from the U.S. Air Force's Strategic Air Command flew the largest nuclear weapon ever produced, the 20,000-pound Mark 36 hydrogen bomb, from the UK to a Spanish air base. The crew faced challenges with the bomb's impact on the aircraft's center of gravity and had to burn off fuel before landing. The flight took them over the Spanish capital of Madrid, leaving the crew to wonder what onlookers thought. On the return trip, the crew encountered unexpected 200-knot headwinds over the Bermuda Triangle, nearly running out of fuel before landing on the East Coast.

Why it matters

The B-47 Stratojet was a crucial component of the U.S. nuclear deterrent during the Cold War, and this flight highlights the unique challenges and risks involved in transporting the most powerful weapons of the era. The story also provides a rare firsthand account of the operational realities faced by bomber crews during this tense period of history.

The details

The B-47 Stratojet was the world's first swept-wing bomber and the first designed solely for nuclear weapons delivery. In 1959, a B-47 crew from the 19th Bombardment Wing was tasked with flying the massive 20,000-pound Mark 36 hydrogen bomb from the UK to a Spanish air base at Moron, near Seville. This was highly unusual, as nuclear weapons were typically transported by military cargo aircraft. However, the crew decided to fly the bomb directly in their B-47 to avoid the need to unload it from alert status in the UK. This presented challenges, as the bomb completely filled the aircraft's bomb bay and pushed the center of gravity far aft, requiring the crew to burn off fuel from the wingtip tanks before landing.

  • In the summer of 1959, the 19th Bombardment Wing moved its overseas operating location from Fairford, Royal Air Force Base in the UK to Moron, Spain.
  • The crew flew the Mark 36 hydrogen bomb, the largest nuclear weapon ever produced, from the UK to Spain.

The players

Richard 'Butch' Sheffield

A former B-47 bombardier/navigator, B-58 navigator/bombardier, and SR-71 Reconnaissance Systems Officer who recounted the details of this flight in his unpublished memoir.

Jim McCracken

The co-pilot who flew with Richard Sheffield on the return trip from Spain to the U.S.

Mark 36

The 20,000-pound hydrogen bomb, the largest nuclear weapon ever produced, that the B-47 crew transported from the UK to Spain.

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What they’re saying

“In order to get our nuclear weapons to Spain we just flew them in our B-47's. This way we did not have to down load them from our alert status in the UK. Our primary weapon was the Mark 36. It weighed twenty thousand pounds, completely filled the B-47 bomb bay and had a seven-megaton yield. This was the largest nuclear bomb ever produced.”

— Richard 'Butch' Sheffield, Former B-47 Bombardier/Navigator

“When it came time to rotate back home to Little Rock, my CO-pilot, Jim McCracken, and I came up with a way to get home sooner than normal. We would land at the Azores; refuel than were going to fly all the way home on one tank of gas going over Bermuda.”

— Richard 'Butch' Sheffield, Former B-47 Bombardier/Navigator

What’s next

The book 'Ohio to Supersonic: Flying the SR-71 Blackbird to the secret world of the Skunk Works' by Colonel Richard 'E.' Butch Sheffield and Linda Marie Sheffield is scheduled to be published in February and is available for pre-order.

The takeaway

This firsthand account provides a rare glimpse into the operational challenges and risks faced by Cold War-era bomber crews tasked with transporting the most powerful nuclear weapons. It highlights the unique capabilities of the B-47 Stratojet and the ingenuity required to overcome the obstacles of flying such a massive bomb.