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
Hecla-class bomb vessel a survey ship, while "Aetna" and "Thunder" were both used as survey ships. "Sulphur" was also used as a survey ship, at one time being commanded by Edward Belcher who later commanded an expedition in search of John Franklin (though not in "Sulphur"). "Erebus" was one of two ships commanded by James Clark Ross during his exploration of Antarctica and by Franklin on his ill-fated search for the Northwest Passage. The other was the "Vesuvius"-class bomb vessel "Terror". Both ships were lost during this last voyage. Hecla-class bomb vessel The "Hecla" class was a class of bomb vessels of the