RAF Coastal Command was a formation within the Royal Air Force (RAF). It was founded in 1936, when the RAF was restructured into Fighter, Bomber and Coastal commands and played an important role during the Second World War. Maritime Aviation had been neglected in the inter-war period, due to disagreements between the Royal Navy (RN) and RAF over the ownership, roles and investment in maritime air power.

The Admiralty's main concern until 1937 was the return of the Fleet Air Arm to the Royal Navy while the RAF concentrated on the development of a bombing force to provide a deterrent. Coastal Command was referred to as the "Cinderella Service" by A V Alexander, the First Lord of the Admiralty in November 1940. Soon after RAF Coastal Area was elevated to Coastal Command, its headquarters moved from Lee-on-Solent to Northwood in northwest London.

During the Second World War, Coastal Command's most important contribution was the protection of Allied convoys from attacks by the U-boats of the German Kriegsmarine. It also protected Allied shipping from aerial attacks by the Luftwaffe. The main operations of Coastal Command were defensive, defending supply lines in the Battle of the Atlantic, as well as the Mediterranean, Middle East, and African theatres. It operated from bases in the United Kingdom, Iceland, Gibraltar, the Soviet Union, West Africa and North Africa. It also had an offensive capacity; in the North Sea, Arctic, Mediterranean and Baltic, strike wings attacked German shipping carrying war materials from Italy to North Africa and from Scandinavia to Germany.

By 1943 Coastal Command finally received sufficient Very Long Range [VLR] aircraft and its operations proved decisive in the victory over the U-boats. These aircraft were Consolidated B-24 Liberators and from early 1943, these and other Coastal Command aircraft, were fitted with ASV Mark III [air-to-surface vessel] centimetric radar, the latest depth charges, including homing torpedoes, officially classed as Mark 24 mines [nicknamed 'Wandering Annie' or 'Wandering Willie'] and even rockets. The Command saw action from the first day of hostilities until the last day of the Second World War.

Coastal Command completed one million flying hours, 240,000 operations and destroyed 212 U-boats. Coastal Command casualties amounted to 2,060 aircraft to all causes. From 1940 to 1945 Coastal Command sank 366 German transport vessels and damaged 134. The total tonnage sunk was 512,330 tons and another 513,454 tons damaged. 10,663 persons were rescued by the Command, comprising 5,721 Allied crew members, 277 enemy personnel and 4,665 non-aircrews. A total of 5,866 Coastal Command personnel were killed in action. During the Cold War, Coastal Command concentrated on anti-submarine warfare preparations against the fleets of the Warsaw Pact. In 1969, Coastal Command was subsumed into the new Strike Command, which had also absorbed the former Bomber, Fighter and Signals Commands and later absorbed Air Support Command, the former Transport Command.

In 1936, almost 18 years after the end of the First World War, there was a change in the command structure of the RAF. Several Expansion Schemes were heading at such pace to re-arm the British military in face of the Nazi threat that "Area" formations were now to be called "Commands". Fighter and Bomber Areas became Fighter and Bomber Commands and Coastal Area was renamed Coastal Command. Its headquarters was located at Lee-on-Solent. Air Marshal Sir Arthur Longmore, Air Officer Commanding (AOC) RAF Coastal Area oversaw the renaming and handed over command to Air Marshal Philip Joubert de la Ferté on 24 August 1936.

In March 1935 the threat from Nazi Germany prompted a series of expansion schemes which pushed the number of squadrons up to 163 (as per Expansion Scheme M, the last before the outbreak of war) and the number of aircraft to 2,549. The scheme was never fully implemented, and Scheme F, 124 Squadrons and 1,736 aircraft, was the only scheme that ran its full course. It did produce modern aircraft and it made adequate provision for reserves (75 per cent) but again, the bomber forces received no less than 50 per cent which averaged 57 per cent over all schemes. Maritime air units never made up more than 12 per cent of British air strength. From a pre-expansion strength of just five squadrons, four of which were flying boats, the figure of maritime squadrons rose to 18 by September 1939, with a strength of just 176 aircraft. Some 16 of these were allocated to trade defence but given Trenchard's policy (which was still in place after his retirement) of developing bombers for the maritime arm which could bolster the air offensive, most were not specialised anti-submarine warfare (ASW) aircraft. The Air Ministry was thoroughly uninterested in any aircraft which fell outside the bomber function.

Joubert was highly critical of the Air Ministry's attitude to his service. In 1937 several exercises were carried out by Coastal Command in co-operation with submarines against the Home Fleet to judge the surface fleet's defence against submarine and air attack. Despite the experiences of the First World War, no attention was paid to the problem of attacking submarines from the air as part of trade protection measures. Owing to misplaced faith in the imperfect ASDIC invention which was never intended to detect surface-running submarines, it appeared the Royal Navy no longer considered U-boats a threat to Britain's sea lanes. The Air Ministry, keen to concentrate on strategic air forces, did not dispute the Admiralty's conclusions and Coastal Command did not receive any guidance from the Air Ministry. The saving grace for both services was the construction of the Combined Headquarters which enabled rapid collaboration in maritime operations. This was one of the few successes in organisation and preparation made before the outbreak of war.