The Palomares accident occurred on 17 January 1966, when a United States Air Force B-52G bomber collided with a KC-135 tanker during mid-air refueling at 31,000 feet (9,450 m) over the Mediterranean Sea, near the Spanish village of Palomares in Almería province. The collision destroyed the tanker, killing all four crew members, and caused the bomber to break apart, resulting in the deaths of three of its seven crew members. The B-52G was participating in Operation Chrome Dome, a Cold War airborne alert mission involving continuous flights of nuclear-armed bombers.
At the time of the accident, the B-52G was carrying four B28FI Mod 2 Y1 thermonuclear bombs. Three of these bombs fell on land near Palomares; the conventional explosives in two detonated upon impact (there was no nuclear explosion triggered), dispersing plutonium and contaminating approximately 2 square kilometers (0.77 sq mi) of terrain. The fourth bomb fell into the Mediterranean Sea and was recovered intact after an extensive 80-day search involving the U.S. Navy, including the use of submersibles such as DSV Alvin. A local fisherman, Francisco Simó Orts, witnessed the bomb's descent into the sea and assisted in its recovery.
In response to the contamination, the U.S. and Spanish authorities conducted cleanup operations, removing approximately 1,750 tons of radioactive soil, which was shipped to the United States for disposal. Despite these efforts, residual contamination persisted, leading to ongoing monitoring and a 2015 agreement between Spain and the U.S. to further remediate the area. As of 2025, some contaminated land remains, and the cleanup has not been fully completed.
Politically, the accident prompted Spain to ban U.S. flights carrying nuclear weapons over its territory. The Palomares accident, along with the similar 1968 Thule Air Base B-52 crash, contributed to the termination of Operation Chrome Dome. Despite its significance, the town of Palomares has no official monument commemorating the event, although a street named "17 January 1966" serves as a reminder.
The B-52G began its mission from Seymour Johnson Air Force Base, North Carolina, carrying four B28FI Mod 2 Y1 thermonuclear bombs on a Cold War airborne alert mission named Operation Chrome Dome. The flight plan took the aircraft east across the Atlantic Ocean and Mediterranean Sea towards the European borders of the Soviet Union before returning home. The lengthy flight required two mid-air refuelings over Spain.
At about 10:30 am on 17 January 1966, while flying at 31,000 feet (9,450 m), the bomber commenced its second aerial refueling with a KC-135 out of Morón Air Base in southern Spain. The B-52 pilot, Major Larry G. Messinger, later recalled,
We came in behind the tanker, and we were a little bit fast, and we started to overrun him a little bit. There is a procedure they have in refueling where if the boom operator feels that you're getting too close and it's a dangerous situation, he will call, "Break away, break away, break away." There was no call for a break away, so we didn't see anything dangerous about the situation. But all of a sudden, all hell seemed to break loose.
The planes collided, with the nozzle of the refueling boom striking the top of the B-52 fuselage, breaking a longeron and snapping off the left wing, which resulted in an explosion that was witnessed by a second B-52 about a mile (1.6 km) away. All four men on the KC-135 and three of the seven men on the bomber were killed.
Those killed in the tanker were boom operator Master Sergeant Lloyd Potolicchio, pilot Major Emil J. Chapla, co-pilot Captain Paul R. Lane, and navigator Captain Leo E. Simmons.
On board the bomber, navigator First Lieutenant Steven G. Montanus, electronic warfare officer First Lieutenant George J. Glessner, and gunner Technical Sergeant Ronald P. Snyder were killed. Montanus was seated on the lower deck of the main cockpit and was able to eject from the plane, but his parachute never opened. Glessner and Snyder were on the upper deck, near the point where the refueling boom struck the fuselage, and were not able to eject.
Four of the seven crew members of the bomber managed to parachute to safety: in addition to pilot Major Messinger, aircraft commander Captain Charles F. Wendorf, copilot First Lieutenant Michael J. Rooney, and radar-navigator Captain Ivens Buchanan successfully bailed out. Buchanan received burns from the explosion and was unable to separate himself from his ejection seat, but he was nevertheless able to open his parachute, and survived the impact with the ground. The other three surviving crew members landed safely several miles out to sea.
The Palomares residents carried Buchanan to a local clinic, while Wendorf and Rooney were picked up at sea by the fishing boat Dorita. The last to be rescued was Messinger, who spent 45 minutes in the water before he was brought aboard the fishing boat Agustin y Rosa by Francisco Simó. All three men who landed in the sea were taken to a hospital in Águilas.
Under United States military nuclear-incident terminology, the event is categorised as a Broken Arrow, the flagword for a nuclear weapons accident and a more serious category than a nuclear weapons incident (flagword Bent Spear). This classification reflects the loss and destruction of nuclear weapons, the non-nuclear detonation of two weapons on land, and the actual occurrence of radioactive contamination.
The weapons lost during the accident were four B28FI Mod 2 Y1 thermonuclear bombs.
The letters FI indicated B28 bombs configured in the full fuzing internal configuration. A full fuzing capability means the weapons could be delivered via all bomb delivery options, including free-fall airburst, retarded airburst, freefall groundburst and laydown groundburst delivery. In this configuration, the W28 warhead was fitted between a Mk28 Mod 3F shock-absorbing nose and a Mk28 Mod 0 FISC rear end containing a parachute. The shock-absorbing nose enabled the weapon to survive laydown delivery, while the parachute slowed the weapon down in retarded airburst and laydown delivery.
The Mod 2 nomenclature indicates the hardened version of the weapon designed to survive laydown delivery; earlier Mod 0 and Mod 1 weapons could not survive the forces involved. The Y1 nomenclature indicates a W28 warhead with a yield of 1.1 megatonnes of TNT (4,600 TJ).
The aircraft and weapons fell to the ground near the fishing village of Palomares, part of the Cuevas del Almanzora municipality in Almeria province, Spain. Three of the weapons were located on land within 24 hours of the accident—the conventional explosives in two had exploded on impact, spreading radioactive contamination, while a third was found relatively intact in a riverbed. The fourth weapon could not be found despite an intensive search of the area—the only part that was recovered was the parachute tail plate, leading searchers to postulate that the weapon's parachute had deployed, and that the wind had carried it out to sea.
On 22 January, the Air Force contacted the U.S. Navy for assistance. The Navy convened a Technical Advisory Group (TAG), chaired by Rear Admiral L. V. Swanson with Dr. John P. Craven and Captain Willard Franklyn Searle, to identify resources and skilled personnel that needed to be moved to Spain.