This was the British designation for fighter-escorted daylight bombing raids by light and medium bombers of No. 2 Group of RAF Bomber Command against targets in German-occupied northern Europe (10 January 1941 onward).
The object of the raids was to inflict damage on these targets, but more importantly to use the threat of such damage to lure German fighters up against the escorting British fighters, and so cause high levels of attrition in the strength of the Jagdgeschwadern (fighter wings) left in North-West Europe from spring 1941 onward.
The first such operation was flown on 10 January 1941, when a force of Bristol Blenheim light bombers of No. 114 Squadron, escorted by nine squadrons of fighters, attacked targets in the Foręt de Guines.
A typical ‘Circus’ might include as few as six bombers and as many as 300 fighters, but the British lost more aircraft than the Germans, and the concept also failed in other objective of compelling the Germans to withdraw fighter units from other theatres for the air defence of northern France.
Similar undertakings were 'Ramrod' similar to 'Circus' but with the intention of destroying the target, 'Ranger' large-scale incursion into German airspace with the object of degrading the German fighter strength, 'Roadstead' low-level attack on coastal shipping, and 'Rhubarb' small-scale freelance fighter mission against ground targets of opportunity.