a smaller calibre gun or an autocannon, or an anti-tank missile launcher, or a combination of weapons. A modern self-propelled gun mounts a large artillery gun but less armour. Lighter vehicles may carry a one-man turret with a single machine gun, occasionally the same model being shared with other classes of vehicle, such as the Cadillac Gage T50 turret/weapons station. The size of the turret is a factor in combat vehicle design. One dimension mentioned in terms of turret design is "turret ring diameter" which is the size of the aperture in the top of the chassis into which the turret is seated. Land fortifications In 1859, the Royal Commission on the Defence of the United Kingdom were in the process of recommending a huge programme of fortifications to protect Britain's naval bases. They interviewed Captain Coles, who had bombarded Russian fortifications during the Crimean War, however Coles repeatedly lost his temper during the discussion and the commissioners failed to ask him about the gun turret that he had patented earlier in that year, with the result that none of the Palmerston Forts mounted turrets. Eventually, the Admiralty Pier Turret at Dover was commissioned in 1877 and completed in 1882. In continental Europe, the invention of high explosive shells in 1885 threatened to make all existing fortifications obsolete; a partial solution was the protection of fortress guns in armoured turrets. Pioneering designs were produced by Commandant Henri-Louis-Philippe Mougin in France and Captain Maximilian Schumann in Germany. Mougin's designs were incorporated in a new generation of polygonal forts constructed by Raymond Adolphe Séré de Rivières in France and Henri Alexis Brialmont in Belgium. Developed versions of Schumann's turrets were employed after his death in the fortifications of Metz. In 1914, the Brialmont forts in the Battle of Liège proved unequal to the German "Big Bertha" 42 cm siege howitzers, which were able to penetrate the turret armour and smash turret mountings. Elsewhere, armoured turrets, sometimes described a cupolas, were incorporated into coastal artillery defences. An extreme example was Fort Drum, the "concrete battleship", near Corregidor, Philippines; this mounted four huge 14-inch guns in two naval pattern turrets and was the only permanent turreted fort ever constructed by the United States. Between the wars, improved turrets formed the offensive armament of the Maginot Line forts in France. During the Second World War, some of the artillery pieces in the Atlantic Wall fortifications,