September 3, 1940, Corallo, under command of captain Loris Albanese, was sent to patrol an area 60 miles south of Crete, between Gaudo and Alexandria. At 18:00 on September 17 Corallo sighted in the position a zigzagging British column heading towards Alexandria. The British force was made up of the aircraft carrier , battleship escorted by five destroyers returning to Alexandria after bombarding Derna and Benghazi. At 18:30 Corallo launched two torpedoes from 1,500 meters against and immediately dove down to 80 meters. After 75 seconds two loud explosions were heard, but no ship, however, was hit. Corallo was then subjected to depth charge attacks by the destroyers which went on for 3 hours. The submarine suffered some damage which impaired her operational efficiency, and two crew members died in the attack. Since the damage to submarine could not be repaired by means available at sea, Corallo was forced to interrupt her mission and headed to Tobruk which she reached on September 18, 1940. On November 5, 1940, Corallo and four other submarines (, , and ) were deployed about 90 miles south-east of Malta with the task of intercepting a British convoy, part of Operation "Coat". Corallo and other submarines formed a barrier with a 20 to 30 miles spacing between them. Corallo, however, did not detect any enemy vessels. On January 21, 1941, Corallo and patrolled off the northern Tunisian coast. Corallo had to abort her mission almost immediately due to a failure, and the submarine had to return to the base. In February 1941 she was on patrol north of Cape Bougaroun, but engine problems forced the submarine to return to the base. In April 1941 she patrolled south of Sardinia, but her mission was cut short again, this time because of the adverse weather conditions. In May 1941 she patrolled around 50 miles west of the island of La Galite without any sightings. In July 1941 Corallo was involved in another uneventful patrol southwest of Sardinia. In October 1941 she was posted off Cap Zebib, but still without success. On November 3, 1941, Corallo under command of captain Andreani was deployed west of Malta as a protective screen for a large Italian "Beta" convoy travelling to Libya. Her job was to detect and report any British naval movements west of Malta, and attack the sighted ships when possible. On November 9, 1941, the "Beta" convoy was