21 March 1945: the date of one of the RAF's most daring and difficult low-level raids.
The target: Shell House in the centre of Copenhagen, which the Gestapo had commandeered as their headquarters. Here they were collecting more and more damaging information about the Danish Resistance which was in danger of being wiped out.
To destroy the Gestapo records meant precision bombing at its most accurate, for not only was Shell House in the middle of a heavily populated area but the Germans had put captured Resistance leaders in cells on the top floor - as hostages against possible attack from the air.
Air Chief Marshal Sir Basil Embry, other senior RAF officers who took part in the raid and wartime members of the Danish Resistance tell of the success - and tragedy - of that day.

The Commanders - Marshal of the RAF Sir Arthur Harris: Tues, 9.25 pm BBC1.
The Shell raid: a justifiable risk?: p 12