The fort was constructed by James Stanley, the 7th Earl of Derby and Lord of Mann in 1645, during the English Civil War, to protect the then busy port of Derbyhaven.

[1][2][3] For about three centuries the "great guns," smooth-bore cannon of brass or cast iron constituted an integral part of the defences in the Isle of Man.

Each harbour around the Island presented its own defensive problem, and in the solutions devised for them it is possible to see the defenders' appreciation of changing circumstances and the limitations of their weapons.

Realising its strategic importance therefore, a battery was constructed on St Michael's Isle to protect the harbour of Derbyhaven.

[1][2][3] Whilst the addition of improved firepower at the fort in 1645 can be seen in a positive light, it did not however in itself solve the defensive problem of Derbyhaven.

[1][2][3] Following the ending of the Napoleonic Wars the forts around the Isle of Man fell into decline and subsequently their strategic importance to the defence of the Island became irrelevant.