Naval mine ship, HMHS "Britannic", which was the sister ship of the RMS "Titanic." During World War II, the U-boat fleet, which dominated much of the battle of the Atlantic, was small at the beginning of the war and much of the early action by German forces involved mining convoy routes and ports around Britain. German submarines also operated in the Mediterranean Sea, in the Caribbean Sea, and along the U.S. coast. Initially, contact mines (requiring a ship to physically strike a mine to detonate it) were employed, usually tethered at the end of a cable just below the surface of the
Yongfeng-class coastal defense ship raised the ship and rearmed it with Japanese guns to enter Japanese service on October 15, 1938, renamed "Asuka" (飛鳥). "Asuka" first served as a torpedo-boat mothership but eventually, in 1940, served as a liaison ship until it was sunk by American aerial attack on May 7, 1945 in the Huangpu River. Specification: "Yongji" is the 2nd ship of "Yongfeng"-class coastal defense ship built by China itself. Construction begun in 1911, the same year as its sister ship "Yongjian", but due to the Xinhai Revolution, construction was delayed and not until seven years later in 1918 was "Yongji" finally completed.