 Though "Iku-Turso" had not had much chance of using its torpedoes, the experiences from other Finnish subs were that the Italian torpedoes used (Finnish designation T/40) were unreliable.During 1942, "Iku-Turso" was upgraded with new 12-hydrophone listening arrays and equipped with a depth charge rack capable of carrying 4 depth charges.The submarine was further modified by streamlining the tower and moving the 20 mm gun up to the tower.