SS Ultonia was a British passenger-cargo vessel built in 1898 in Wallsend-on-Tyne by C. S. Swan & Hunter. It was sunk by a German torpedo in 1917.

SS Ultonia launched on 4 June 1898, measuring 500 feet (150 m) by 57.4 feet (17.5 m) by 33.9 feet (10.3 m), 8,845 gross tonnage with engines by Sir C. Furness, Westgarth & Co, Middlesbrough. Originally launched for cargo and cattle, it was fitted with third-class accommodation for 675 passengers in 1899, launching its first passenger voyage on 28 February from Liverpool to Queenstown to Boston.

Departing Boston on one of these voyages on 5 August 1899, the Ultonia hit a ledge just outside the main channel of Boston Harbor at Nantasket Roads, which was the typical route at the time. This area is now called the Ultonia Ledge, located a mile and a half southeast of Boston Light, and is as shallow as 21 feet (6.4 m) at mean lower low water according to modern nautical charts. This event spurred the alteration of ships' courses in the area to avoid the ledge, the dredging of Nantasket Roads to a depth of 35 feet (11 m) to be safe for large steamships, and also the later dredging of the wider northern approach via President Roads, which is the now the main channel for large ships entering or exiting Boston Harbor.

In 1902, it was refitted to accommodate 120 second-class passengers, and 2,100 third-class passengers, increasing its tonnage to 10,402 gross. In 1915, it was refitted to carry up to 2,000 horses.

On 27 March 1917, Ultonia collided with the British collier SS Don Benito in the Atlantic Ocean (49°35′N 6°44′W / 49.583°N 6.733°W / 49.583; -6.733). Don Benito sank.

During World War I, Ultonia was torpedoed and sunk in the Atlantic Ocean 190 miles from Fastnet, Ireland, on 27 June 1917 by the Imperial German Navy submarine SM U-53 under Captain Hans Rose. One life was lost in the attack.

• List of the largest ships hit by U-boats in World War I
• List of shipwrecks in June 1917
• William Thomas Turner

48°25′00″N 11°23′00″W / 48.4167°N 11.3833°W / 48.4167; -11.3833