October 1943
| 1 | October | -The US 5th Army entered Naples. -Soviet forces crossed the Dniepr River. |
| 3 | October | German forces landed on Cos Island in the Aegean. |
| 4 | October | -Admiral Andrew B. Cunningham replaced Admiral Pound as First Lord at the Admiralty. -Free French forces liberated Corsica. |
| 7 | October | Admiral of the Fleet, Sir Dudley Pound, resigned for health reasons. He passed away two weeks later. |
| 9 | October | German forces evacuated the Kuban peninsula (Crimea). |
| 13 | October | The Badoglio government declared war on Germany. Italy became a co-belligerent though technically not an ally. |
| 21 | October | Admiral John Cunningham became Commander-in-Chief Mediterranean. |
Italian submarine patrols in the Mediterranean during October 1943
| Zoea (23-26 October) Pt.1 | Corridoni (26-30 October) Pt.1 | Atropo (26-30 October) Pt.1 |
| Zoea (27-29 October) Pt.2 | Manara (27 October…) | Menotti (28-31 October) Pt.1 |
| Corridoni (30 October…) Pt.2 | Atropo (31 October…) Pt.2 |
The tanker Olterra was towed from Algeciras to Gibraltar after Spanish authorities agreed to release her after the Italian Armistice. Of her crew, only her engineer Paolo Donegri remained on board, and on 11 October, he told her story to the British. She had only two human torpedoes left, and one of them had been scuttled beyond repair.
The submarines Onice, Platino, and Vortice were used to supply power to the city of Naples.
On 16 October, the submarines Atropo, Corridoni, Menotti, and Zoea were transferred from Malta to Haifa, where they would be used as transport submarines to supply the Dodecanese islands. They were joined by Alagi, Bragadino, and Galatea by the end of the month. These submarines would constitute a new flotilla: Gruppo Sommergibili del Levante or Grupsom Levante. Upon arrival in Haifa, Galatea was redirected to Alexandria to be used for anti-submarine training, while Bragadino, with serious engine defects, was towed back to Taranto.
Zoea (T.V. Rodolfo Bombig) was the first submarine to accomplish a supply mission. She sailed from Haifa on 23 October and reached Leros three days later. She was followed by Atropo (T.V. Aredio Galzigna) and Corridoni (T.V. Giandaniele Asquini) on the 26th and Menotti (T.V. Enzo Mariano) on the 28th of the month.
Manara (T.V. Gaspare Cavallina) carried out her first and only special mission, sailing from Brindisi on the 27th and landing three groups of agents behind enemy lines in northern Adriatic. The bad state of her engines prevented further participation in these activities, and she was relegated to training duties.