Fortification of Island Terrain: Second World War German Military Engineering on the Channel Island of Jersey, a Classic Area of British Geology

Abstract

The 116 km² Channel island of Jersey was fortified by the British intermittently from the 13th to 19th centuries, and by the Germans more intensively during the Second World War — to form part of Hitler’s ‘Atlantic Wall’. British castles, forts and towers were sited to counter potential amphibious attack by the French. German forces (which at their peak totalled about 11,500 troops, supported by a construction workforce of a further 6,000 men) adapted many of these sites to counter amphibious attack by the Allies, augmenting them with batteries of heavier coastal artillery together with an impressive sequence of associated observation towers/posts, about 100 fortified infantry defence areas, a series of anti-tank walls and ditches, an extensive minefield complex, tunnels for storage and shelter, central and local command/control centres, and numerous anti-aircraft guns. Siting of fortress installations was influenced mainly by geomorphology, but the Germans made significant use of military geologist expertise to predict foundation characteristics, ensure adequate supplies of potable water, and locate sources of the considerable quantities of aggregate required for construction. Geologically the island forms part of the Armorican Massif more extensively exposed in the adjacent areas of Brittany and Normandy, a classic ‘hard rock’ terrain composed largely of metasediments and volcanics of 587–582 million years (late Proterozoic) age intruded by later Proterozoic and Ordovician granites and associated igneous rocks, modified overall by much later features of Quaternary erosion and sedimentary deposition. Jersey contrasts with the 6 km² Jurassic limestone Rock of Gibraltar, famous for over 200 years as a British fortress outpost, in geology as well as size and occupation history, but other aspects of their fortification were constrained by similar general principles.