Olympic-class ocean liner of 29 coal-fired steam boilers in six compartments. However, "Olympic"s boilers were adapted for firing by oil at the end of the First World War, which reduced the number of engine crew required from 350 to 60. The "Olympic"-class ships were long, displacing normally (their draft at this displacement being ), and their tonnage was around 45-46,000 GRT. "Olympic" became the largest ship in the world when it was completed in May, 1911 before losing the title to its sister "Titanic" when she was completed in April, 1912. After the loss of "Titanic" the third sister ship "Britannic" claimed the
Sister ship an . The most famous sister ships were the White Star Line's , and . As with some other liners, the sisters worked as running mates. Other sister ships include the Royal Caribbean International's and . "Half-sister" refers to a ship of the same class but with some significant differences. One example of half-sisters are the First World War-era British s where the first two ships had four guns, but the last ship, , had two guns instead. Another example is the American s of the Second World War that came in "long-hull" and "short-hull" versions. Notable airships include the