The Civil War and Oliver's Battery, Tresco
In 1646 the Royalist forces in Scilly surrendered to Parliamentary troops but in September 1648 the garrison rebelled against the Governor and declared for the King. Scilly became a major privateering base preying on British and Dutch vessels. Parliament’s attempts to counter this proved largely ineffective, but in March 1651 a squadron of Dutch ships under Maarten Tromp was sent to obtain the release of ships. Parliament feared that the Dutch might also try to capture the islands, and so an expedition commanded by Robert Blake was sent to retake them.
Blake’s troops were eventually landed on Tresco near the Old Blockhouse after some heavy fighting, and then they seem to have marched across the island to take King Charles’ Castle. With the island in Parliament’s hands a gun battery, Oliver’s Battery, was built at Carn Near, overlooking where boats today land visitors to Tresco at low tide. Set in front of the large, rocky outcrop, this earthwork battery had positions for two guns that could shell ships in St Mary’s Pool and the Road, and this forced the Royalists to surrender in June 1651.
For more information on Scilly’s rich military history read Defending Scilly by Mark Bowden and Allan Brodie (English Heritage 2011 £9.99)
http://www.english-heritage.org.uk/publications/defending-scilly/