SS Irma was a 1,322-ton steamship built by the British shipyard Sir Raylton Dixon & Co. Ltd. in Middlesbrough in the north-east of England. She was delivered to the Norwegian passenger ship company Det Bergenske Dampskibsselskab of Bergen in 1905. Irma served the company until she was attacked and sunk by two MTBs belonging to the Royal Norwegian Navy on 13 February 1944.

After delivery, Irma served on the Bergen–Newcastle route until she was transferred to Norway in the autumn of 1921 to provide voyages for tourists to North Cape and Spitsbergen during the summer season. In 1927, she was put on the Norway–Hamburg route, replacing SS Neptun and SS Mira. A new heating system was installed in 1913 and wireless radio in 1914. A new streamlined rudder was fitted in 1928. In 1931, she joined the Hurtigruten route in Norway, replacing SS Hera after the latter's shipwreck in March that year. Irma was rebuilt in 1931, and again in 1932. In a series of upgrades she received a refrigeration system in 1933, improved navigational equipment in 1938 and an echo sounding device in 1939. The ship was very popular with her passengers, her smoking salon receiving particular praise. She had only one serious accident in the pre-war years, which occurred when she hit a reef off Kabelvåg in the Lofoten islands in 1937. Although suffering leaks in her port side, Irma managed to make port in Kabelvåg and put ashore all of her 120 passengers. Repairs were carried out at a shipyard in Bergen.

Following the outbreak of the Finnish-Soviet Winter War in late November 1939, Norway reinforced her northern border forces, and Irma was dispatched from the Nordland port of Mosjøen on 11 December 1939 to transport Norwegian troops to the border with the Soviet-occupied Finnish district of Petsamo. The troops belonged to the first battalion of Infantry Regiment 14. The original orders from the military were that the entire battalion was to board Irma for the journey to Finnmark, even though the ship was only certified to carry less than half the number of people involved. After vigorous protests from both soldiers and officers over safety concerns and overcrowding, the original plan was abandoned and only half the battalion shipped on Irma, the rest leaving some days later on the fellow Hurtigruten steamer Richard With. The incident with Norwegian conscripts being subjected to attempts to force them to board an overcrowded ship led to a public outcry in Mosjøen. The Mosjøen newspaper Helgeland Arbeiderblad published an article shortly after the incident criticising the Norwegian military leadership's handling of the troop transport.

When the German invasion of Norway began on 9 April 1940, Irma was at Bergen, one of the Norwegian cities captured by German forces that day. She continued to sail along the Norwegian coast with passengers and freight during the German occupation.

On 13 February 1944 Irma was sailing northwards from Bergen to Trondheim under the command of Captain Sofus Strømberg. That day she had a crew of 43 and was carrying 40 Norwegian passengers as well as probably seven Germans. Her cargo consisted of freight, mail and 1,800 tons of herring.

At 18:37 Irma, sailing in Hustadvika Bay by Hestskjær Lighthouse off the port of Kristiansund in Møre og Romsdal, was attacked by HNoMS MTB 627 and HNoMS MTB 653. She suffered a large explosion in the bow area. The initial explosion, which caused massive damage, was followed by another amidships shortly thereafter, the ship immediately starting to sink. The Norwegian cargo ship SS Henry was in the same area, and was also sunk shortly after Irma. In addition to what turned out to be torpedo strikes, the two ships were subjected to in total 2,034 rounds of heavy machine gun fire. 61 Norwegian civilians died on Irma, and another two on Henry. Only 25 people survived the sinking of Irma, and for days afterwards dead bodies washed ashore on the Norwegian coast as far north as Namsos. Before Henry sank she had been able to launch two of her lifeboats and these first saved several of her crew before moving to the location where Irma had gone down and rescuing survivors from floating rafts. An hour after the attack the tugboat Hopplafjord passed the scene and rescued further survivors from rafts. The fishing boat Sveggøy also rescued 12 survivors from a raft.

Irma's sinking constituted the last major loss for the Hurtigruten service during the Second World War, with numerous coastal passenger ships having up to that point been lost to mines, air and submarine attacks since the April 1940 German invasion of Norway.

The wreck of Irma was discovered by a geological survey vessel on 3 November 1999 north of Averøya at a depth of 200 metres (660 ft).