The Bréhon Tower (Fort Brehon) is accessible only by boat and sits on Bréhon Rock, an island in the Little Russell channel about 1.5 km northeast of St Peter Port, Guernsey, between the port and the islands of Herm and Jethou.

Thomas Charles de Putron (1806–1869) built the oval tower of granite from Herm, completing the work in 1857.

[3] In the tenure (1803–1813) of Lieutenant Governor General Sir John Doyle, there were plans to erect a guardhouse on Bréhon, but nothing came of these.

Lieutenant Governor Major-General Sir William Francis Patrick Napier proposed a number of works, including the establishment of a fort on Bréhon.

This led to the construction of several defensive structures, including towers and forts, in the Channel area.

[7] Bréhon Tower's role was to guard the shipping channel between Guernsey and Herm, and help protect the harbour of St Peter Port.

When the garrison fired the cannons for the first time, the concussion created a fracture that extended from top to bottom.

[1] In World War II, German forces installed a 10.5 cm (4.1 in) coastal defence gun in a new embrasure cut in the north wall.

[1] On 14 May 1943, RAF Spitfires of the Czechoslovak-manned 312 and 313 Squadrons made a low-altitude attack on a flotilla of 12 E-boats in St Peter Port in an operation called Roadstead 2.

[12][13] A year later, on 22 May 1944, Bréhon Tower's guns shot down Flight Lieutenant Hugh Percy of 610 Squadron.