The Sea Cadet Corps has its roots in the 1850’s when a number of orphanages were established to look after children orphaned after the Crimean War and were run with the help of sailors returning from the Crimea. An organisation was then established called the 'Naval Lads' Brigades'. In 1899 HM Queen Victoria graciously presented a £10 note to the Windsor Unit for the purchase of uniforms. From 1999, the anniversary of this event, 25 June, has been declared the Birthday of the Sea Cadets.
In 1910 the Navy League decided to sponsor a small number of these independent units as the Navy League Boys’ Naval Brigade. This slowly expanded with the addition of other formations such as Sea Scout groups.
In 1919 the Admiralty granted recognition of the by now 34 Brigades subject to an annual efficiency inspection and the title 'Navy League Sea Cadet Corps' was adopted. In 1937 Lord Nuffield gave £50,000 to fund the expansion of the Corps and by 1939 at the start of the war there were nearly 100 units with some 10,000 cadets. In 1941 the Navy League instigated a scheme to train Sea Cadets in TS Bounty for service in the wartime navy and, as a result, the Admiral Commanding Reserves took over the training role and, in January 1942, HM King George VI became Admiral of the Corps. Officers were granted appointments in the RNVR and the corps was renamed the Sea Cadet Corps. In the same year the Girls’ Naval Training Corps (GNTC) was formed. In 1947 the Navy League refused the Admiralty's offer to take over the Sea Cadet Corps entirely but agreed to co-sponsorship, with the Admiralty agreeing to supply uniform, boats, training facilities and limited pay to adult staff who retained appointments in the RNVR (later to be RNR). A Sea Cadet Council was set up to govern the Corps with input from the Navy League and Royal Navy. Meantime the GNTC continued to expand and by the late 1950s had been renamed the Girls’ Nautical Training Corps.
The first Marine cadet sections were established in 1955, and in 1963 the GNTC was affiliated to the Sea Cadet Council. In 1976 the Navy League was renamed the Sea Cadet Association and the Admiral Commanding Reserves title lapsed. His duties were transferred to the Commander-in-Chief Naval Home Command in Portsmouth. The Sea Cadet Charter was revised and replaced by a Memorandum of Agreement.
In 1980 girls were allowed to join the SCC, and the GNTC ceased to exist as a separate entity. By 1992 girls were fully integrated into the Sea Cadet Corps, and Junior Sea Cadets aged from 10-12 year olds were also introduced into the Corps, although the Junior Sea Cadets are not formally recognised by the Ministry of Defence.