At 02:19 on 21 November 1970, an American helicopter deliberately flew itself into the trees inside a North Vietnamese prison camp twenty-three miles from Hanoi. Its rotor blades chewed through forty-foot foliage and it came down hard in a courtyard roughly the size of a volleyball court. Fourteen Green Berets walked out of the wreck.

Twenty-seven minutes later they were gone again, having killed the guards, searched every cell, and lost nobody.

They had also found nothing. The prisoners they came for had been moved four months earlier.

Why a helicopter had to be wrecked

The plan's most famous feature was not bravado. It was arithmetic.

The Son Tay compound was tiny and ringed by trees over forty feet high. There was no way to land outside and fight your way in — there were 12,000 North Vietnamese troops within five miles, and the whole operation depended on being finished before any of them could react.

So the assault element had to arrive inside the walls. The largest helicopter that would physically fit in that courtyard was the HH-3E Jolly Green Giant, and even it would lose its rotor blades on the way down. The aircraft was therefore written off before it ever launched: fly it in, crash it deliberately, blow it up on the way out.

The raiders rehearsed the landing 31 times on a full-size mock-up at Eglin Air Force Base in Florida, part of 170 practice sessions and over 1,000 flight hours.

Transports flying at the edge of a stall

The navigation problem was solved in a way that still sounds improbable. Two C-130E(I) Combat Talons — the designation MC-130E did not yet exist in 1970 — led the helicopters to the target using terrain-following radar.

The difficulty is that a C-130 cruises much faster than an HH-3E. The solution was to fly the Hercules at 105 knots with 70 degrees of flap, barely above stalling speed, while the helicopters tucked in and drafted off the transports' wingtips to gain enough airspeed to keep station.

Meanwhile the US Navy flew a diversion: roughly twenty A-7 Corsairs and A-6 Intruders off USS Oriskany and USS Ranger, dropping flares over Haiphong and dropping no bombs at all — described as the largest carrier night operation of the war. North Vietnamese air defences fired at least 36 SA-2 missiles into the confusion. Two MiG-21s sat at Phúc Yên and were never cleared to take off.

Simons had kept the destination secret until that moment. In the same briefing he told them the mission was something American prisoners had a right to expect from their fellow soldiers. The room, by all accounts, erupted.

"Negative items"

Inside the compound, Captain Richard Meadows put a bullhorn to his mouth seconds after the crash landing.

Nothing came back. The cells were empty. Meadows radioed the prearranged code phrase for the outcome nobody had planned for: negative items.

The prisoners — somewhere between 55 and 65 men, depending on which account you follow — had been relocated on 14 July 1970 to another camp closer to Hanoi, reportedly because Son Tay's wells had become unusable. American intelligence had not detected the move.

A second element, Greenleaf, had meanwhile landed 400 metres off target and assaulted a building intelligence had labelled a secondary school. It was a barracks. The mistake may have been useful: it suppressed a reaction force that would otherwise have been on the compound within minutes.

A perfect failure

Almost every account since — including the National Museum of the US Air Force's own — draws the same distinction: the execution was close to flawless, and the intelligence failed completely.

The tactical results argue for themselves. A joint force flew 116 aircraft into the most heavily defended airspace on earth at night, put men on the ground inside an enemy prison twenty-three miles from the enemy capital, spent 27 minutes there, and came home having lost one aircraft they had always intended to lose and one F-105 whose crew was recovered.

The strategic effects were real even without prisoners. North Vietnam consolidated its scattered POW camps into larger facilities in Hanoi, which ended years of solitary confinement for many Americans and let them organise, communicate and support each other. Several later said the raid transformed their captivity, and the knowledge that their country had come for them mattered more than the empty cells.

It was the first joint operation run under the direct control of the Chairman of the Joint Chiefs of Staff. The lessons — particularly about who owns special operations and how they are commanded — fed directly into the creation of US Special Operations Command in 1987.

The raiders wore an unofficial patch showing a mushroom and the letters KITD/FOHS: Kept In The Dark, Fed On Horse ——. It is on display today at the National Museum of the US Air Force, next to a piece of barbed wire recovered from the camp wall in 1995.

A full account of the planning and execution of the raid.

The US Army Center of Military History’s own briefing on the operation.

Terry Buckler, the youngest man on the raid, describing it in his own words.

Sources: National Museum of the United States Air Force; C.V. Glines, Air Force Magazine; US Army ARSOF History; Wikipedia.