Q: In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.
Passage: With government subsidies promised, initially at $385,000 a year, and with the backing of the leading investment bank Brown Brothers, Collins founded the New York and Liverpool United States' Mail Steamship Company, familiarly known as the Collins Line. He immediately embarked on an ambitious steamship construction program. The first of the four Collins Line ships, SS Atlantic, was launched in 1849 and began service in April 1850. Her three sister ships, Pacific, Arctic and Baltic, were all in service before the end of 1850. The four, all constructed of wood, were broadly similar in size and performance; Arctic was marginally the largest, at 284 feet (87 m) in length and 2,856 tons by American custom house measurement. The new Collins Line steamers were about 25 percent larger than the biggest of the Cunard ships, and were soon outperforming them; crossings in ten days became routine. Arctic entered service on October 26, 1850. The luxurious standards of its passenger accommodation contrasted with those experienced by Charles Dickens, who crossed the Atlantic in Cunard's Britannia in 1840. Dickens found his Britannia cabin dark and cramped, "a thoroughly hopeless, and profoundly preposterous box", while the bleak saloon was "a long narrow apartment, not unlike a gigantic hearse". In Arctic, according to a seasoned transatlantic passenger, her cabins "in comfort and elegance surpassed that of any merchant vessel Great Britain then possessed", while the main saloon had "an air of almost Oriental magnificence".Under her captain, James Luce, a 49-year-old veteran of thirty years at sea, Arctic became the most celebrated of the Collins ships. Her record eastbound crossing, from New York to Liverpool in nine days, seventeen hours in the winter of 1851–52, earned her the title of the "Clipper of the Seas". Luce was admired by passengers as much for his social qualities as for his seamanship; a reporter for Harper's New Monthly Magazine wrote approvingly: "If you ever wish to cross the Atlantic, you will find in the Arctic one of the noblest of ships, and in Captain Luce one of the best of commanders".
A:
What were the three sister ships of the one that entered service on October 26th, 1850?