The Sultanate of Egypt and Sudan was a short period (1914 — 1922) during which the former Khedivate was a British Protectorate, and the ruler’s title was changed from khedive to sultan.
There was a decent variety, from a stamp-collecting point of view, of issues in this short period. Various overprinted Egyptian stamps were used, and there were some with no overprint at all — these sometimes had the value and denomination inscribed in English.
The overprinted varieties were generally overprinted in English and Arabic. In one popular form, issued several times during the Sultanate’s existence, the English was ‘O.H.H.S.’, meaning On His Highness’ Service. (In 1913 there was such a stamp without an Arabic overprint.) Although the Sultanate didn’t officially exist until 1914, the first stamps of this kind were issued in 1907.
See also: Egypt rare stamps for philatelists and other buyers
Today, there are usually several of these stamps available at any time to collectors, and Egypt, Sudan, or Britain stamp enthusiasts can find a few pieces to add to their collections.
