This was the British first bombing raid on a German urban area rather than a specific industrial target (16/17 December 1940).
The operation was planned as the first of the proposed 'Abigail' series of raids schemed in response to the devastating 'Mondscheinsonate' German air raid of 14/15 November 1940 on Coventry, and was schemed on the basis of a concentrated attack by 200 of more bombers to destroy a significant portion of the selected town or city and not purely an industrial objective. The three possible targets were Bremen ('Abigail Jezebel'), Düsseldorf ('Abigail Delilah') and Mannheim ('Abigail Rachel').
'Abigail Delilah' was the initial selection by Air Marshal Sir Richard Peirse’s Bomber Command, but the forecast of poor weather over Düsseldorf led to a late change to 'Abigail Rache' against Mannheim, which was attacked by a total force of only 134 bombers (61 Vickers Wellington, 35 Armstrong Whitworth Whitley, 29 Handley Page Hampden and nine Bristol Blenheim aircraft), of which only 103 bombed. Considerable success was initially claimed for the raid, which cost the British seven aircraft and 17 men, but photographic reconnaissance on 21 December revealed that the bombing had in fact been widely dispersed and caused only modest damage.