Bréhon Tower

The Bréhon Tower 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 built the oval tower of granite from Herm, completing the work in 1857.Although not strictly a Martello tower, Bréhon represents the final evolution of the basic design of the Martello tower. In 1914 the War Office transferred ownership of Bréhon Tower to the States of Guernsey. During the German occupation of the Channel Islands, German forces placed coastal defence and anti-aircraft guns on the tower. Today, although the site is open to visitors, the tower is closed. The tower holds a light operated by the Guernsey Harbour Authority. The island is home to a breeding colony of common terns.

Source: Wikipedia