civilian deaths, especially when passenger ships were sunk. It also violated the Prize Rules of the Hague Convention. Furthermore, the U-boats also sank neutral ships in the blockade area, either intentionally or because identification was difficult from underwater. This turned neutral opinion against the Central Powers, as countries like the U.S. and Brazil suffered casualties and losses to trade. In early 1917, Germany declared unrestricted submarine warfare, including attacks without warning against all ships in the "war zone", including neutrals. This was a major cause of U.S. declaration of war on Germany. The U-boat campaign ultimately sank much of British merchant shipping and caused shortages of food and other necessities. The U-boats were eventually defeated by grouping merchant ships into defended convoys. This was also assisted by U.S. entry into the war and the increasing use of primitive sonar and aerial patrolling to detect and track submarines. Mediterranean Some limited sea combat took place between the navies of Austria-Hungary and Germany and the Allied navies of France, Britain, Italy and Japan. The navy of the Ottoman Empire only sortied out of the Dardanelles once late in the war during the Battle of Imbros, preferring to focus its operations in the Black Sea. The main fleet action was the Triple Entente attempt to knock the Ottoman Empire out of the war by an attack on Constantinople in 1915. This attempt turned into the Battle of Gallipoli which resulted in a Triple Entente defeat. For the rest of the war, naval action consisted almost entirely in submarine combat by the Austrians and Germans and blockade duty by the triple entente. Black Sea The Black Sea was mainly the domain of the Russians and the Ottoman Empire. The large Russian fleet was based in Sevastopol and it was led by two diligent commanders: Admiral Andrei Eberhardt (1914–1916) and Admiral Alexander Kolchak (1916–1917). The Ottoman fleet on the other hand was in a period of transition with many obsolete ships. It had been expecting to receive two powerful dreadnoughts fitting out in Britain, but the UK seized the completed and with the outbreak of war with Germany and incorporated them into the Royal Navy. The war in the Black Sea started when the Ottoman Fleet bombarded several Russian cities in October 1914. The most advanced ships in the Ottoman fleet consisted of two ships of the German Mediterranean Fleet: the powerful battlecruiser and the