Axis naval co-operation started after the signing of the Pact of Steel in June 1939 with meetings in Friedrichshafen, Germany, and an agreement to exchange technical information.

[5] Initially, their activity did not meet much success; unacquainted with Atlantic weather conditions, Italian submarines sighted convoys but lost contact and failed to make effective reports.

As co-operation between the two navies was not working well, Dönitz decided to reassign the Italian boats to the southern area where they could act independently.

[3][6] Dönitz considered the Italians as displaying "great dash and daring in battle, often exceeding that of Germans", but less toughness, endurance and tenacity.

Gazzana-Priaroggia's boat, Leonardo da Vinci, was the top-scoring non-German submarine of World War II, with 17 ships sunk totalling 120,243 GRT.

[10][11] Another notable Betasom commander was Salvatore Todaro, known for his habit of towing to safety the lifeboats containing the survivors of ships he had sunk.

[12] Italian submarines operating in the Atlantic sank 109 Allied merchant ships totalling 601,425 tons, and lost 16 boats.

The base was bombed by the British on several occasions, especially in 1940 and 1941, but no significant damage was suffered, except for the sinking of the barracks ship Usaramo.

[15] The remaining BETASOM boats ended their last offensive patrol in 1943, after which Bagnolini, Barbarigo, Comandante Cappellini, Finzi, Giuliani, Tazzoli and Torelli were adapted to carry supplies from the Far East as part of an agreement between Italy and Germany.

Italy had agreed to convert the surviving Betasom submarines, larger than German U-Boats and thus more suited for transport missions, in exchange for the transfer from the Kriegsmarine to the Regia Marina of an equal number of Type VIIC U-Boats, which would be manned by Italian crews and thus continue Italian participation in submarine operations in the Atlantic.

The U-Boats ceded to Italy were still training in Danzig with their new Italian crews when the armistice was announced and were immediately retaken by the Kriegsmarine.

Perla, Guglielmotti, Brin, Argo, Velella, Dandolo, Emo, Otaria, Mocenigo, and Veniero made the passage.

The submarine pens have proved to be infeasible to demolish due to their massive reinforced construction which had been designed to withstand aerial bombardment.