HMS Hilary was a Booth Line passenger steamship that was built in Scotland in 1908 and operated scheduled services between Liverpool and Brazil until 1914.

In the First World War she was an armed merchant cruiser (AMC) until a U-boat sank her in the Atlantic Ocean in 1917.

In the first decade of the 20th century these services included regular sailings between Liverpool and Manaus, 1,000 miles (1,600 km) up the Amazon River.

[4] Caledon Shipbuilding & Engineering Company of Dundee launched Lanfranc on 18 October 1906 and completed her in February 1907.

[11] She and her sisters were the largest ships in Booth's fleet until Scotts Shipbuilding and Engineering Company launched Hildebrand in 1911.

[10] At 0725 hrs Hilary was 40 nautical miles (74 km; 46 mi) west of Lerwick when SM U-88 torpedoed her, hitting her port side just forward of her boiler room.

Her wireless telegraph (W/T) operator tried to send a distress signal from her auxiliary radio, but its accumulators lacked enough charge to transmit.

After 0830 hrs only three men remained aboard: Captain Dean, Lieutenant Commander Wray and an Assistant Steward called Edwards.

Dean, Wray and Edwards then manned a 6-inch gun and tried to train it on U-88, but the torpedo impacts had damaged the gunsight and prevented them from getting a good aim at the submarine.

After the ship sank, men were redistributed between the boats to prevent overloading and the Carley floats were abandoned.

[10] In 1930 Nature published an article that claimed Captain Dean and several of his officers sighted a sea serpent about 70 nautical miles (130 km) southeast of Iceland on 22 May 1917, three days before U-88 torpedoed Hilary.

The creature was described as black and smooth, with a snake-like neck and no protrusions except a dorsal fin about 4 ft (1.2 m) high.