The British Empire possessed enough resources and naval might to maintain a strong presence in the area and replace most losses by redeploying ships.

The sea was vital for the supply of the Italian and German forces in North Africa, as well as the maintenance of Malta as a British offensive base.

Supermarina (the naval staff of the Regia Marina), at the request of Comando Supremo (supreme command of the Italian armed forces), made an emergency plan to shift supplies using warships.

The 4th Division was ordered to pass north-west of the Aegadian Islands and then head for Cape Bon and follow the Tunisian coast; the ships would keep a speed of 22–23 kn (41–43 km/h; 25–26 mph) to conserve fuel and deliver it at Tripoli.

[3] In the afternoon of 12 December, a CANT Z.1007 bis of the Regia Aeronautica spotted the four destroyers heading east at an estimated speed of 20 kn (37 km/h; 23 mph), 60 mi (97 km) off Algiers.

Supermarina was immediately informed but calculated that, even in the case the destroyers would increase their speed to 28 kn (52 km/h; 32 mph), they would not reach Cape Bon until around 03:00 on 13 December, about one hour after the 4th Division.

[4] Following new Ultra decodes a new reconnaissance aircraft spotted Toscano's ships at sunset on 12 December, after which the 4th Destroyer Flotilla was directed to intercept the two cruisers, increasing speed to 30 kn (56 km/h; 35 mph).

Arriving from astern, under the cover of darkness and using radar, the British ships sailed close inshore and surprised the Italians, who were further out to sea, by launching torpedoes from short range.

Di Giussano was left dead in the water with fires raging; the crew struggled to keep the ship afloat but she also had to be abandoned, breaking in two and sinking at 4:20, with the loss of 283 men.

The course change was ordered more than 30 minutes after the cruisers had been spotted; Toscano may have wanted to mislead the reconnaissance aircraft about his real course, wait for it to leave and then turn again for Tripoli.

He may have thought, from the aircraft noise, that torpedo bombers were coming and he wanted to get into waters farther away from the shore and from Italian minefields to gain freedom of manoeuvre.

Toscano ordered his gunners to stand by; he may have known that Allied destroyers were astern of his ships and he wanted to avoid presenting his stern to them because his aft turrets were obstructed by the fuel barrels.