[2] On 10 June 1940, the date of the Italian entry into World War II, Pegaso was part of VI Torpedo Boat Squadron at the naval base in Naples, which she formed together with her sister ships Orsa, Procione and Orione.

On 2 July 1940 Procione, Orsa, Orione and Pegaso escorted from Tripoli to Naples (a return route) two transport ships, Esperia and Victoria.

[4] On 6 July 1940, Pegaso took part in the escort of the first large convoy to Libya (named Operazione TCM): setting sail from Naples at 7.45pm, the convoy was made up of troop transports Esperia and Calitea (carrying respectively 1,571 and 619 soldiers) and the modern cargo motorships Marco Foscarini, Francesco Barbaro (added on 7 July after arriving from Catania with the escort of the torpedo boats Abba and Pilo[4]) and Vettor Pisani (whose load consisted of 232 vehicles, 5,720 t of fuels and lubricants and 10,445 t of other supplies); together with the four ships of the XIV Torpedo Boat Squadron, the light cruisers Bande Nere and Colleoni and the X Destroyer Squadron (destroyers Maestrale, Grecale, Libeccio, and Scirocco).

[6] Between 1 and 3 March 1941 Pegaso, Orione and a third torpedo boat, Clio, escorted a convoy (steamers Amsterdam, Castellon, Maritza and Ruhr) from Naples to Tripoli carrying supplies for the Afrika Korps.

[7] From 5 to 7 March Pegaso, Orione and the auxiliary cruiser Ramb III escorted the return convoy (Tripoli-Naples) of the steamships Castellon, Ruhr and Maritza.

[9][10] At 04.40 on 24 May she left Naples as escort, together with the destroyer Freccia and the torpedo boats Procione and Orsa, with a convoy made up of troop transports SS Conte Rosso, Marco Polo, Esperia and Victoria.

[3] At 20.40 the British submarine HMS Upholder, after sighting the convoy and approaching, launched two torpedoes: they struck SS Conte Rosso , which sank in ten minutes, dragging 1297 men with it.

[11] On 14 July she escorted from Tripoli to Naples, together with the destroyers Fuciliere, Alpino and Malocello and the torpedo boats Orsa and Procione, the transports Rialto, Andrea Gritti, Sebastiano Venier, Barbarigo and Ankara.

[13] On 10 September the torpedo boats Pegaso, Procione, Orsa and Circe (to which Perseo was added on the 13th) and the destroyers Fulmine and Oriani left Naples escorting a convoy (steamers Temben, Caffaro, Nicolò Odero, Nirvo, Giulia and Bainsizza) bound for Libya, which on 12 September was attacked by British Fairey Swordfish planes of 830 Naval Air Squadron northwest of Tripoli.

[17] On 13 December, as part of the operation "M 41", Pegaso left Taranto on escort duty to Benghazi, together with the destroyers Pessagno and Usodimare, the motor ships Monginevro, Napoli and Vettor Pisani (the "M 41" was however suspended later).

[3][19] In April 1942 Pegaso was most probably responsible for depth charging and sinking the British submarine Upholder, which has posed a persistent threat to the Italian convoys.

[20][21] At 16.00 on 16 April 1942, Pegaso under the command of corvette captain Francesco Acton, received a report from a CANT Z.506 seaplane of the 170th Squadron of the 83rd Maritime Reconnaissance Group based at Augusta, who claimed to have sighted a wake likely caused by the periscope of a submarine.

[24] At 12.30 on 6 August 1942 Pegaso was escorting a convoy about thirty miles southwest of the islet of Gaudo (Crete), when one of the planes of the air escort was seen from aboard the torpedo boat to strafe the sea surface; four minutes later Pegaso detected a submarine under water and then made seven passes, throwing depth charges and finally losing contact: the probable result of this action was the sinking of the British submarine HMS Thorn, at position 34°25′N 22°36′E / 34.417°N 22.600°E / 34.417; 22.600, with no survivors.

[25][26] On 19 October Pegaso (under the command of lieutenant Gian Luigi Sironi) was escorting a convoy from Naples to Tripoli when, at 12.58, the steamship Beppe was torpedoed either by the British submarine HMS Unbending[27] or by aircraft.

Pegaso, while the attack was still continuing, towed the struck ship to Pantelleria, taking it to the protection of the anti-aircraft batteries; at that point, however, a torpedo bomber appearing from behind the hills of the island sank Beppe, frustrating all the efforts made.

[3] At 14.25, about twenty miles south of Marettimo, the convoy was attacked by 8 British bombers, escorted by 12 fighters: hit by two bombs (one of which, however, was a dud), Thorsheimer was immobilized with fire on board.

[30] After the armistice announcement, in the early morning of 9 September 1943, the ship, under the command of frigate captain Riccardo Imperiali, set sail from La Spezia together with Orsa, Orione, Ardimentoso and Impetuoso, followed, at one hour's distance, by the rest of the battle squadron (battleships Italia, Vittorio Veneto and Roma, light cruisers Attilio Regolo, Eugenio di Savoia, Montecuccoli, destroyers Artigliere, Fuciliere, Legionario, Carabiniere, Mitragliere, Velite, Grecale, Oriani) heading for La Maddalena.

During this time, both Pegaso and Impetuoso repeatedly requested information via radio from Supermarina (the Italian navy headquarters) and the other units of the squadron but did not receive any response.

[30] The torpedo boats stopped in the middle of the bay, then, with the crews reduced to a minimum (17 men on Pegaso and 10-11 on Impetuoso), they continued until they reached deep waters over a hundred meters, sufficient to prevent a recovery of the two ships; then - between 05.00 and 06.00 hours on 11 September 1943 - they raised the combat flag, destroyed secret documents and opened portholes, shutters and sea cock valves (another measure adopted on Pegaso was to pour all the fuel left into the storage tanks on the port side, in order to increase the list), after that the captains and the men remaining on board took their places on the only two lifeboats left.