Among them were enlargement of the false tower at the top, more modern engines, installation of a radiogoniometer that could be controlled from inside the ship.
[6] The captain of the submarine believed this was a 6987 GRT Republican tanker heading to Alicante under the presumably false name SS Woodford, as the crew appeared to be Romanian.
At the time of Italy's entrance into World War II Diaspro was assigned to the 72nd Squadron (VII Submarine group) based at Cagliari.
On September 1, during British Operation "Hats" Diaspro was on patrol in an area between Cape Spartivento and the island of La Galite.
[2][8] On November 9, 1940, she left Cagliari to patrol off the island of La Galite along with four other submarines with the task of intercepting a British convoy, part of Operation "Coat" but failed to sight any enemy ships.
Located about 315 miles from the island of La Galite, she was only able to detect a minor ship from the British force, but failed to attack it.
[11] Diaspro was on three missions in February, May and June 1941, east of the island of La Galite, about twenty miles north of Cape Blanc, and south of Sardinia, respectively, but without any success.
In the early afternoon of July 21, 1941 Diaspro under command of captain Antonio Dotta sailed from Cagliari to her area of operation about 55 miles off Cape Bougaroun.
Diaspro closed in to within 1,000-1,300 meters and at 23:07 launched four bow torpedoes against cruisers, and two minutes later she fired two stern ones at a battleship and an air-carrier.
Two stern torpedoes traveled harmlessly under the destroyer's hull, as they were set to run deeper to hit a larger ship.
HMAS Nestor went on to launch depth charge attack against Diaspro, only causing minor damage to the submarine.
[12] Between the end of July and the beginning of August 1941, Diaspro was deployed to patrol an area southwest of Sardinia with three other submarines to intercept a British convoy, part of Operation "Style" but she did not sight any ships.
She then received an order to move south, and in fact, at 6:17 on September 29, she sighted enemy ships about forty miles northwest of Philippeville in the position 37°32′N 6°45′E / 37.533°N 6.750°E / 37.533; 6.750.
[14] From April 1 to September 10, 1942 Diaspro was assigned to the Submarine School at Pula where she participated in 32 training missions before being reassigned to active duty at Cagliari.
On November 8, 1942 Diaspro was involved in an underwater collision with another Italian submarine Alagi, near Cape Bougaroun, while approaching her patrol sector.
[2] On September 7, 1943, as part of the Zeta Plan, Diaspro was deployed along with ten other submarines in the Tyrrhenian Sea, first in the Gulf of Salerno, then off Gaeta to intercept an anticipated Anglo-American landing in southern Italy.