On the morning of 21 March 1945, twenty de Havilland Mosquitos came in over Copenhagen at rooftop height, so low that Danes on the streets could see the crews' faces. Their target was the Shellhus — the Gestapo's headquarters in the heart of the city, where captured resistance fighters were held on the top floor as human shields. The raid was a triumph of precision. It was also one of the most heartbreaking accidents of the air war.

Operation Carthage destroyed the Gestapo's Danish nerve centre and let prisoners walk out of a burning building. And then, a mile and a half away, it killed 86 schoolchildren. Both things are true, and neither cancels the other.

A raid the RAF did not want to fly

The request came from the Danish resistance, and it was desperate. The Gestapo was closing in; comrades were being tortured for names inside the Shellhus, and the dossiers stored there could unravel the whole network. Destroy the building, the resistance argued, and you destroy the files and free the prisoners in one stroke.

The RAF said no at first. Bombing a single building in a crowded city centre, at low level, with friendly prisoners inside it, was close to impossible — the kind of mission where a few feet or a few seconds separated success from catastrophe. Only after repeated pleas did 2 Group agree, drawing on the same pinpoint-raid expertise that had smashed open the prison walls at Amiens a year earlier.

Destroying the Shellhouse: the Mosquito raid on Copenhagen.

Wave one: a bullseye

Flying from RAF Fersfield in Norfolk and escorted by P-51 Mustangs, the Mosquitos crossed the North Sea at wave height to stay under the radar. The first wave hit the Shellhus almost perfectly. Bombs punched into the lower floors, the building caught fire, and in the chaos prisoners on the top floor scrambled clear — some down ladders, some through the smoke. Fifty-five German soldiers and dozens of Danish Gestapo collaborators died inside; eighteen prisoners got out alive.

The mast, the school, and the smoke

Then came the accident that has haunted the raid ever since. As the first wave pulled away, one Mosquito clipped a tall mast, was crippled, and crashed near the Jeanne d'Arc School — a Catholic girls' school about 1.5 kilometres from the target. Its wreckage burned fiercely.

Minutes later the second and third waves arrived, saw thick black smoke rising, and did what aircrew are trained to do: they bombed the fire, believing it marked the target their leaders had already hit. It was not the Shellhus. It was the school. Eighty-six children and eighteen adults, many of them nuns, were killed. The precision that made Carthage possible also made its worst error unstoppable once it began.

The full story of the most ambitious — and most tragic — low-level raid of the war.

A hard kind of memory

Operation Carthage achieved its military aim. The Gestapo's Danish operation never fully recovered, and lives were saved because the files burned. But in Denmark the raid is remembered less for what it destroyed than for whom it could not spare. The dead children are commemorated across Copenhagen to this day.

That is the uncomfortable truth of pinpoint bombing, then and now: the same low, daring accuracy that lets an aircraft hit one building in a city is also what puts it a heartbeat away from hitting the wrong one. Carthage is where that truth was written in the plainest and saddest terms.

Contemporary footage and analysis of the Copenhagen raid.

Sources: Wikipedia (Operation Carthage); Imperial War Museums; The People's Mosquito; Defense.info.