Fort Blockhouse had its beginnings as a military base in 1431 when Henry VI authorised a tower to be built on the Gosport side of Portsmouth Harbour. By 1714, the tower had grown into a fort with much the same outward characteristics as it has now, and by 1813 it was described as being "complete". Since then many alterations and additions have been made, notably between the two world wars when most of the existing buildings were constructed or rebuilt.
The only records of the guns of the Fort being fired in anger are in 1642 and again during World War 2. The first occasion was during the Civil War, when Parliament troops who had captured Southsea Castle were fired upon. The aim of the gunners of the time may have been influenced by the presence of a grog shop close to the entrance of the Fort, for it is recorded that one cannon-ball landed way off-target on St Thomas' Church in Old Portsmouth. During World War 2 the fort's anti-aircraft defences were reinforced by two of the saluting guns, which were being converted by the Engineers to fire a mixture of old iron and were manned by a volunteer crew of stokers. Battle Honours, however, went to the pom-pom mounted below the Sub-Signal Station, which shot down an enemy aircraft over the Solent on 16th August, 1940. The saluting guns, the earliest of which was manufactured in 1886, are still used regularly for ceremonial gun salutes.
The Navy moved into Fort Blockhouse in 1905 for the purpose of establishing a "Submarine Boat Station". The Fort was taken over from the Royal Engineers, who had been in occupation since 1873, and who were at the time responsible for submarine mining. Another nautical connection with REs is their regiment march, a variation of which is well known in the Service as "The Oggy Song".
The name DOLPHIN is taken from the hulk of the sailing ship, built in 1882, of that name which was berthed alongside the fort from 1906 until 1923 as a depot for submarines. Since then her name has become synonymous with the Submarine Service - dolphins form its distinctive badge and DOLPHIN has long come to be regarded as the Alma Mater of an important arm of the Royal Navy.
The Queen's Colour was presented by HM the Queen to the Submarine Service on Monday, 8th June 1959, and hangs in a place of honour in the Wardroom.
To mark the Diamond Jubilee of the Submarine Branch, and in recognition of the long association between the Submarine Branch and the Borough of Gosport and of the contribution made by the branch to the history of the Royal Navy, the Honorary Freedom of the Borough of Gosport was conferred on the Submarine Branch on 7th July 1961.