The Dodecanese campaign was the capture and occupation of the Dodecanese islands by German forces during World War II. Following the signing of the Armistice of Cassibile on 3 September 1943, Italy switched sides and joined the Allies. As a result, the Germans made plans to seize control of the Dodecanese, which were under Italian control. The Allies planned to use the islands as bases to strike against German targets in the Balkans, which the Germans aimed to forestall.

Beginning in early September 1943, invading German troops defeated both the Italian garrison in the Dodecanese and British forces sent to support them, aided by the fact that Allied units were operating without sufficient air cover. Most of the Dodecanese islands fell to German forces within two months, resulting in one of Germany's last major victories during the conflict. The Germans continued to occupy the Dodecanese islands they had captured until the end of the war in 1945, when they surrendered to British forces.

The Dodecanese island group lies in the south-eastern Aegean Sea, and had been under Italian control since the Italo-Turkish War in 1911. During Italian rule, the strategically well-placed islands became a focus of Italian colonial ambitions in the Eastern Mediterranean. Rhodes, the largest of the islands, was a major military and aerial base. The island of Leros, with its excellent deep-water port of Lakki (Portolago), was transformed into a heavily fortified aeronautical base, "the Corregidor of the Mediterranean", as Benito Mussolini, the Italian leader, boasted. An early British attempt to contest Italian control of the Dodecanese, codenamed Operation Abstention, was thwarted in February 1941, when Italian forces recaptured the island of Kastellorizo from British commandos.

After the Battle of Greece in April 1941 and the Allied defeat in the Battle of Crete in May 1941, Greece and its many islands were occupied by the Axis powers. With the defeat of Axis forces in the North African campaign in May 1943, Winston Churchill, the British Prime Minister, envisaged an operation to capture the Dodecanese and Crete, to deprive the Axis of excellent forward bases in the Mediterranean and to apply pressure on neutral Turkey to join the war. This would promote a favorite idea of Churchill's, that of a "route through the Dardanelles to Russia as an alternative to the Arctic convoys." In the Casablanca Conference, the go-ahead was given and Churchill ordered his commanders to have plans ready for 27 January 1943.

Operation Accolade called for a direct attack on Rhodes and Karpathos, with three infantry divisions, an armored brigade and support units. Landings at Crete, which was too well fortified and had a strong German garrison, were dropped. The main problem faced by the planners was the difficulty of countering Fliegerkorps X of the Luftwaffe because of a lack of air cover, as American and British aircraft were based in Cyprus and the Middle East. This challenge was exacerbated by the demands of the upcoming Allied invasion of Sicily. The Americans were sceptical about the operation, which they regarded as aiming mostly at post-war political benefits for Britain and an unnecessary diversion from the Italian campaign. They refused to support it, warning the British that they would have to go it alone.

As an Italian surrender became increasingly possible, in August 1943 the British prepared to take advantage of a possible Italian–German split, in the form of a smaller version of Accolade. A force based on the 8th Indian Infantry Division was assembled and American assistance in the form of P-38 Lightning long-range fighter squadrons was requested. As a result of the Quebec Conference and the US refusal to assent to British plans, the forces and ships earmarked for Accolade were diverted barely a week before the surrender of Italy in the Armistice of Cassibile on 8 September.

On the announcement of the armistice, the Italian garrisons on most of the Dodecanese Islands either wanted to change sides and fight with the Allies or go home. Anticipating the Italian armistice, German forces, based largely in mainland Greece, had been rushed to many of the islands to maintain control. The German forces were part of Army Group E commanded by the Luftwaffe General Alexander Löhr. The most important German force in the Dodecanese was the 7,500-strong Sturm-Division Rhodos (Assault Division Rhodes), commanded by Generalleutnant (Lieutenant-General) Ulrich Kleemann. This division was formed during the summer on the island of Rhodes, which was the administrative center of the Dodecanese Islands and had three military airfields. Because of this, Rhodes was the principal military objective for both sides.

On 8 September 1943, the Italian garrison on the island of Kastelorizo surrendered to a British detachment, which was reinforced during the following days by ships of the Allied navies. The next day, a British delegation, headed by George Jellicoe, was dropped by parachute on Rhodes, to persuade the Italian commander, Ammiraglio Inigo Campioni, to join the Allies. Swift action by the German forces forestalled the Allies; Kleemann attacked the 40,000-strong Italian garrison on 9 September and forced it to surrender by 11 September. The loss of Rhodes dealt a critical blow to Allied hopes. Many Italian soldiers in the Aegean were tired of the war and had become opposed to Mussolini. Italian Fascist loyalists remained allied to Germany in the Greek campaign. German forces in Greece convinced 10,000 Italians in the Aegean to continue to support their war effort.