Shortlived defence of Tresco
Oliver's Battery is a ruined artillery battery on the island of Tresco. It was built by the Parliamentarian admiral, Sir Robert Blake, after he invaded Tresco in April 1651 during the years of the interregnum. It was used to bombard the neighbouring island of St. Mary's, which was still held by an opposing Royalist army, and forced its surrender several weeks later. The battery comprised a triangle of ramparts, constructed using earth and rubble, which, combined with the natural stone features on the site, produced a substantial, if crude, fortification. It is now ruined, and owned by the Duchy of Cornwall.
Oliver's Battery was built in the interregnum following the English Civil War. The Isles of Scilly had supported Charles I during the conflict between 1642 and 1646, and, after a short period in Parliamentary control, the islands rebelled in favour of Charles in 1648. The islands became a base for Royalist privateers, and Parliament became concerned that the Dutch, then hostile to England, might counter the piracy by occupying the islands, gaining a foothold that they could then use against England. In 1651 Parliament sent Sir Robert Blake in charge of a naval task force to retake the islands.
Blake arrived in April 1651 and set about invading the island of Tresco. Taking the harbour of Old Grimsby in an amphibious assault on 18th April, he then bypassed the northern fortress of King Charles's Castle and marched south, intending to use Tresco as a base for taking the neighbouring island of St. Mary's, approximately 1.2 miles away.
When Blake reached Carn Near on the south end of Tresco, he constructed an artillery position for a battery of three guns overlooking the channel between the island and St. Mary's, as well as the harbour of St. Mary's Pool, hoping to pressure the Royalists into surrender. The work was carried out rapidly between 19th April and 4th May, possibly reusing the site of a Bronze Age burial cairn. When the battery began firing on 4th May, one of the guns exploded causing two deaths, but the bombardment soon recommenced and St. Mary's agreed to surrender several weeks later on 23rd May.
Oliver's Battery is on a hill overlooking the island of St. Mary's to the south-east. It is triangular in shape, the sides of which are roughly 82 feet by 98 feet by 98 feet in length. The battery was entered from its north-western side, and in the north-east corner there was a small building, approximately 20 feet by 11 feet, which may have been a store or a temporary gun magazine. The artillery pieces were located in the south-eastern corner of the battery, where a gun platform, 23 feet in diameter, occupied the highest part of the fortification.
The battery is surrounded by an earth and rubble bank, incorporating natural outcrops of stone, between 15 feet and 26 feet wide, and 6 feet 7 inches high externally. On the west and south sides the ramparts are protected by a ditch, typically 15 feet wide and 2 feet deep. The historian Mark Bowden considers the fortification to be "substantial but relatively crude", probably a result of the speed with which the building work was carried out.
At the most southerly point of the island.
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The Isles of Scilly
Cromwell's Castle King Charles's Castle Old Blockhouse Tresco