Built between 1854 and 1856 on the Brehon Rock, in the middle of the Little Russel between Guernsey and Herm, this is the last local fortification built during the Napoleonic period. It was constructed by Thomas Charles Du Putron from Herm granite at a cost of £8098.
The tower is actually elliptical in shape rather than round. When it was finished it had five 18 pound guns mounted on top, and became home to 35 artillerymen.
Like the breakwaters at St.Catherine in Jersey and Braye Harbour in Alderney, the tower was built in response to the program of fortification that Napoleon was carrying out on the nearby ports of Cherbourg, Granville and St.Malo. Towards the latter part of the 19th century, when Britain and France had settled their differences, the guns were removed from the tower.
In 1914, ownership of the tower passed into the hands of the States of Guernsey.
During the Second World War, the occupying forces mounted an anti-aircraft gun on Brehon Tower. The gun crew shot down several planes, including one of their own; a Focke-Wulfe FW190.