The Old Blockhouse, New Grimsby
OS grid reference :- SV 881 159
King Henry VIII ordered the construction of a series of fortifications along the south coast to defend Enghland against his French and Spanish enemies, but Scilly was left neglected.
The Old Blockhouse, also known as the Dover Fort, overlooks Old Grimsby harbour and was probably the earliest of the defences on Tresco. It was one of a series of forts built on the islands during the reigns of his successors, the boy king Edward VI and Queen Mary I. The building consists of a square, paved platform which could have accommodated three guns. On the south side there are the remains of a built-in locker, presumably for gunpowder, and attached to the west side there is a small room with two windows and a fireplace which offered shelter for the garrison.
During the Civil War, a Royalist garrison was defending the islands in 1651 against attack by a Parliamentarian fleet under the command of Admiral Robert Blake. Blake landed at St Helen's Pool in April 1651 and set about taking the island of Tresco. The blockhouse was used by Royalists to mount heavy gunfire on Parliamentary forces attacking the adjacent stretch of Tresco's north eastern coastline.
He attacked the harbour of Old Grimsby on 18 April, Blake planned to use a force of men in small boats, but they landed on the wrong island and had to be recalled to the ships. The following day Blake's soldiers landed on the beaches beneath the blockhouse, fierce fighting ensued and the Parliamentarians were driven back to their ships. Blake's men made a further landing which was also met with vigourous resistance, the guns of the blockhouse were probably turned on the landing parties. About 15 of the assault force were killed, but the guns of Blake's ships guns had a longer range than those of the blockhouse and Old Grimsby fell.
Blake then moved inland and struck against Kings Charles' Castle. By 20th April 1651, Tresco was in Parliamentarian hands. After capturing Tresco's fortifications, he used the island as a base to attack the main Royalist stronghold defended by Sir John Grenville, the Royalist Governor of the Island at Star Castle on St Mary's. The Blockhouse was later replaced by a much stronger gun fort, Cromwell's Castle, on the other side of the island, though it was still considered serviceable in the eighteenth century.
The Old Blockhouse is now in the care of English Heritage.