Operation Jubilee or the Dieppe Raid (19 August 1942) was a disastrous Allied amphibious attack on the German-occupied port of Dieppe in northern France, during the Second World War. Over 6,050 infantry, predominantly Canadian, supported by a regiment of tanks, were put ashore from a naval force operating under the protection of Royal Air Force (RAF) fighters.

The port was to be captured and held for a short period, to test the feasibility of a landing and to gather intelligence. German coastal defences, port structures and important buildings were to be demolished. The raid was intended to boost Allied morale, to demonstrate the commitment of the United Kingdom to re-open the Western Front, and to support the Soviet Union, which was fighting on the Eastern Front.

The Luftwaffe made a maximum effort against the landing as the RAF had expected, and the RAF lost 106 aircraft (at least 32 to anti-aircraft fire or accidents) against 48 German losses. The Royal Navy lost 33 landing craft and a destroyer. Aerial and naval support was insufficient to enable the ground forces to achieve their objectives. The tanks were trapped on the beach and the infantry was largely prevented from entering the town by obstacles and German fire.

After less than six hours, mounting casualties forced a retreat. Within ten hours, 3,623 of the 6,086 men who landed had been killed, wounded, or taken prisoner. 5,000 were Canadians, who suffered a 68% casualty rate, with 3,367 killed, wounded or taken prisoner. The operation was a fiasco in which only one landing force temporarily achieved its objective, and a small amount of military intelligence was gathered.

Both sides learnt important lessons regarding coastal assaults. The Allies learnt lessons that influenced the success of the Normandy landings. Artificial harbours were declared crucial, tanks were adapted specifically for beaches, a new integrated tactical air force strengthened ground support, and capturing a major port at the outset was no longer seen as a priority. Churchill and Mountbatten both claimed that these lessons had outweighed the cost. The Germans also believed that Dieppe was a learning experience and made a considerable effort to improve the way they defended the occupied coastlines of Europe.

In the aftermath of the Dunkirk evacuation of the British Expeditionary Force in May 1940, the British started on the development of a substantial raiding force under the umbrella of Combined Operations Headquarters. This was accompanied by the development of techniques and equipment for amphibious warfare. In late 1941, a scheme was put forward for the landing of 12 divisions around Le Havre, assuming a withdrawal of German troops to counter Soviet success in the east. From this came Operation Rutter to test the feasibility of capturing a port by an opposed landing, the investigation of the problems of operating the invasion fleet and testing equipment and techniques of the assault.

After its victory in the Battle of Britain in 1940 and the Luftwaffe having switched to night bombing in the autumn of 1940, the day fighters of Royal Air Force Fighter Command were "a force without an immediate mission". Without anything else to do, the day fighters of RAF Fighter Command were in the spring of 1941 deployed on a series of search-and-destroy missions of flying over France to engage the Luftwaffe in combat. In the second half of 1941, the aerial offensive over France was greatly stepped up, leading to the loss of 411 British and Canadian aircraft. In the spring of 1942, the Luftwaffe deployed the new Focke-Wulf Fw 190 fighter to its airfields in France.

The Fw 190 was superior to the Supermarine Spitfire Mk V and Hawker Hurricane Mk IIs used by the British and Canadian pilots and losses over France increased. The RAF was convinced it was winning the air war, believing that the loss of 259 Spitfires over France in the first six months of 1942 were justified by the reported destruction of 197 German aircraft in the same period. A major problem for the RAF was that the Luftwaffe German fighter pilots declined to engage in combat over the French coast and instead operated inland, forcing the British Spitfires to fly deeper into France, using up their fuel, placing them at a disadvantage when the Luftwaffe engaged, and, critically, if RAF pilots had to bail out they would be in enemy occupied territory, i.e. RAF Fighter command was now operating with all the disadvantages the Luftwaffe had to contend with in the Battle of Britain. Thanks to intelligence provided by Ultra, the British knew that if any Allied force attempted to seize a port in France, the Germans would assume it to be the beginning of an invasion and thus the Luftwaffe was to mount a maximum effort. Fighter Command lobbied in early 1942, for a raid to seize a French port to provoke the Luftwaffe into action with the RAF at an advantage.