The island was occupied by France 28 December 1915 (in the cruiser Amiral Charner?). Turkish shore batteries responded by shelling the island, in 1917 succeeding in sinking the HMS Ben-my-Chree.
It was ceded to Italy in 1922. During the 1930s it was a stopover for the planes of Alitalia and Air France.
When Italy capitulated to the Allies in 1943, the island was occupied by British commandos until the middle of 1944, when German forces took over. During the British departure, a fuel dump caught fire and spread to an adjacent ammo dump, whose detonation destroyed half of the homes on the island.
Kastellórizo became part of Greece in 1945. The population, once estimated at 15,000 in 1900, has dwindled to around 250, heavily subsidized so as to forestall territorial claims by Turkey. Much of the population emigrated to Australia, where they are known as "Kassies".
The island has been more visited in recent years, by tourists looking for an isolated Dodecanese island.
Postage stamps
In 1920, the French occupation forces issued stamps of the French Offices in Turkey overprinted O.N.F. / Castellorizo, then with B.N.F. / CASTELLORIZO and then O F / CASTELLORISO oriented vertically. All of these overprints are uncommon, with prices ranging from US$10 up to over US$500 for some types.
Starting in 1922, the Italians overprinted their own stamps with CASTELROSSO. In 1923 they issued a series of five stamps depicting a map of the island and an Italian flag, then went back to more overprints on Italian stamps, with a regular issue in 1924, the Ferrucci issue in 1930, and the Garibaldi issue of 1932. A few types are readily available unused and cost under US$1, but the others, and all used copies, are in the US$5-$10 range.