The submarines in the flotilla suffered from faulty air conditioning, that poisoned crews when submerged, causing several losses.

The capture of Massawa and other Italian ports in the region brought the Flottiglia del mar rosso to an end in April 1941.

After the Flotta d'evasione (evasion fleet) intended for the Indian Ocean, based in the ports of Italian Somaliland proved to be too expensive, Rear Admiral Carlo Balsamo di Specchia-Normandia, the commander of the East African naval squadron, based a smaller force at Massawa.

[2] The base at Massawa and the smaller base at Assab on the Eritrean coast, was convenient for attacks on convoys sailing from the Gulf of Aden through the Red Sea to the Suez Canal, which became much more important after the Mediterranean was closed to Allied merchant ships, forcing them to sail around the Cape of Good Hope.

[4] Italy declared war on 10 June 1940 and the Flotilla tried to attack Royal Navy ships and Allied convoys from Massawa but the British had suspended sailings to the Red Sea on 24 May 1940.

On 19 June, when the submarine engaged the armed trawler Moonstone, all the officers except a midshipman were killed in two shell explosions and the vessel was captured, along with its operational orders and taken to Aden on the same day.

[9] From 19 to 21 September, Leone and Pantera, Battisti and Manin with the submarines Archimede and Guglielmotti, searched for Convoy BN 5 but failed to find it; Bhima (5,280 GRT) was bombed, ran aground and towed back to Aden.

The convoy was about 35 nmi (65 km; 40 mi) north-north-west of Jabal al-Tair Island at 02:19 on 21 October, when the New Zealand cruiser, Leander, sighted two patches of smoke bearing north.

Kimberley closed to 5,000 yd (2.5 nmi; 4.6 km) and at 06:20, Nullo scraped a reef, damaging a propeller and springing a leak.

Fearful that the British were trying to spring ambush, the other Italian ships converged on Sauro and called by wireless for air cover at dawn, reaching port unharmed.

[16] On 14 February, in Operation Composition, 14 Albacore bombers from HMS Formidable attacked Massawa, sinking Moncaliere (5,723 GRT) and damaging other ships and freighters.

Ramb I had departed Suez on 10 June 1940 for Massawa, from where the ship made short cruises along the coast of Eritrea but was mainly used for anti-aircraft defence of the port.

[18] As British troops neared the port, Ramb I and Coburg (7,400 GRT), a German freighter, escaped from Massawa on the night of 20/21 February 1941 and passed into the Gulf of Aden.

At 10:37 a.m., on 27 February, west of the Maldives, the New Zealand cruiser HMS Leander sighted a merchant resembling an Italian Ramb-class fruit carrier (Ramb I).

[19] The cruiser was broad on the beam of Ramb I and at 3,000 yd (1.5 nmi; 1.7 mi; 2.7 km) was an easy target for its guns and torpedoes.

A fire spread and an Italian officer in the water called out to a boarding party that they should not approach the ship, as it was burning and laden with ammunition.

The boarding party laid off and as the fire spread, a big explosion before the bridge shot flames and smoke high into the sky, the ship settling bow first.

As the Italians depleted their fuel at Massawa, the offensive capability of the Red Sea Flotilla declined and it returned to a strategy of a fleet-in-being.

The two remaining ships joined Sauro, Battisti and Daniele Manin on a final raid against Port Sudan on 2 April.

On 11 April, President Roosevelt announced that the Red Sae and the Gulf of Aden we no longer considered to be war zones, allowing US ships to sail in them.

His staff repaired the largest dry dock and pieced together enough machine tool parts to restore machinist operations.