The submarine had participated in the 1940-41 Greco-Italian War. It had sunk one Italian vessel and carried out four war patrols.
Following the German invasion of Greece in April 1941, Katsonis fled to the Middle East with the rest of the fleet. On July 2, 1942, the submarine was damaged while exiting a dry dock at Port Said. Following an overhaul, the submarine went on a further three patrols in the Aegean.
On September 14, while trying to intercept a German troop transport, the submarine was attacked and sunk by the German submarine chaser UJ-2101. Thirty-two men of the crew, including its commander, went down with the submarine, and 15 were captured. Among them was Konstantinos Stamoulis, a survivor who was considered dead for decades. However, Lt Elias Tsoukalas, the ship’s XO, and petty officers Antonios Antoniou and Anastasios Tsigros, managed to swim for 9 hours and reach Skiathos. There they hid and managed to return to Egypt and rejoin the Greek fleet. The historic wreck was found by the Nautilus tanker that was on a mission in the region on July 4.