She was named after the Amba Alagi mountain in Ethiopia, which was at the time part of Italian East Africa The Adua-class submarines were essentially repeats of the preceding Perla class.

[1] For surface running, the boats were powered by two 600-brake-horsepower (447 kW) diesel engines, each driving one propeller shaft.

From 5 to 11 June 1941, Alagi, under command of captain Giulio Contreas, patrolled 20 miles northeast of Ras Azzaz.

[3] At 10:47 on 12 June 1941, while returning to Messina, Alagi was attacked with two bombs and machine guns off Benghazi by a British Sunderland aircraft.

In the late afternoon of 14 January 1942, in the Strait of Sicily, Alagi sighted a British naval formation and at 21:05 launched two torpedoes, which did not hit any targets.

On 8 June 1942, roughly 20 nm North of Cape Bon Alagi, under command of captain Sergio Puccini, fired three torpedoes at a naval column (later identified as friendly convoy from Naples to Tripoli).

One torpedo hit and sunk the Italian destroyer Antoniotto Usodimare in a friendly fire incident [3][4] (141 killed and 165 survivors).

On 12 July 1942 at 20:04, at 34°59′N 35°32′E / 34.983°N 35.533°E / 34.983; 35.533, northwest of Tripoli, Syria, Alagi fired two torpedoes and scored one hit in the engine room of the Turkish tanker Antares (3723 GRT, 1893) on a trip from Iskanderun to Haifa, causing her to be beached on Ruad Island.

[3] On 8 November 1942, while sailing submerged to her area of operation near Bizerta, she collided underwater with another Italian submarine Diaspro and suffered serious damage to her tower and had to turn back and return to Naples.

After a minute and 45 seconds a violent explosion was heard, but no information about this action was ever reported in British official documentation.

[3] In October 1943, Alagi was transferred to Haifa where she was employed as a training unit for British troops and as a shipping vessel for supplies to the Aegean Islands.