April 1943
| April | The situation in Tunisia reached a critical stage for Axis troops. | |
| 22/23 | April | Grand-Admiral Dönitz visited the Betasom base. |
Italian submarine patrols in the Mediterranean during April 1943
| Corridoni (…1 April) Pt.1 | Gorgo (…4 April) | Nichelio (…4 April) |
| Ambra (…5 April) | Wolframio (…11 April) | Acciaio (3-17 April) |
| Argo (3-16 April) | Velella (3-20 April) | Axum (3-13 April) |
| Corridoni (4-7 April) Pt.2 | Brin (11-17 April) | Argento (11-17 April) |
| Platino (11-17 April) | Giada (12-17 April) | Topazio (15 April…) |
| H.8 (15-16 April) | H.2 (15-16 April) | Dandolo (15 April…) |
| Menotti (20-24 April) Pt.1 | Menotti (25-28 April) Pt.2 |
No attacks were carried out by Italian submarines during this month. They were readied for the assault on Italy, which was sure to follow the impending loss of Tunisia. Ascianghi and Diaspro were moved to Ajaccio (Corsica) in an attempt to disperse the submarines in anticipation of an attack on Sardinia or Sicily; later, Bonifacio was also used. At the beginning of the month, Bragadino was the last submarine to stop at Trapani on a return trip from a supply mission to Sousse. In fact, III Grupsom in Messina and VIII Grupsom in Trapani had ceased to exist as offensive bases since November 1942, although Messina would still be used by Italian and German U-boats transiting the Straits until the fall of Sicily.
Before noon on 3 April, Francesco Rismondo (C.C. Francesco Pedrotti) was almost certainly the submarine sighted by HMS Trident as she left La Spezia for anti-submarine exercises. The range was long—7,000 yards—but nevertheless, the British submarine launched a salvo of five torpedoes, a sixth misfired. They must have passed very wide of the mark as the attack was unobserved.
Three days later, Topazio (T.V. Mario Patané) was slightly damaged in a collision with the torpedo-boat Sagittario in Naples harbour.
Wolframio (T.V. Giovanni Manunta) tried to land a commando (one officer and ten other ranks) on the Algerian coast between Cape Carbon and Cape Sigli but gave up after several unsuccessful attempts due to bad weather (5-7 April).
La Maddalena was heavily bombed by the USAAF on 10 April. The heavy cruisers Trento and Gorizia were hit; the former capsized, and the latter was heavily damaged and out of the war. Several smaller vessels were also sunk or damaged. The submarines Sirena (four killed, ten seriously wounded), Mocenigo (one killed, two seriously wounded), Topazio (one missing, one wounded) and Aradam (one wounded), were slightly damaged.
On 19 April, it was La Spezia’s turn to be hit by a heavy air raid. The submarines escaped unscathed, save Ambra, who suffered only minor damage. The destroyer Alpino was sunk, the destroyer F.R.22 (ex French Panthère) was damaged, and several smaller vessels were destroyed or damaged.
On 26 April, while patrolling about seventy-five miles north of Cape Bougaroni, Dandolo (T.V. Aldo Turcio) was seen by the Dutch submarine Dolfijn (Lt Cdr H M.L.F.E. van Oostrom Soede), who could only fire three torpedoes from long range. Turcio saw them in time and turned his submarine away, intending to fire a stern shot. He was prevented from firing his torpedo as the smoke emitted from his engines obscured the target, and the opportunity vanished. The three torpedoes passed harmlessly away, two on the port side and the third on the starboard side.
Atlantic
Italian submarine patrols in the Atlantic and Indian Ocean during April 1943
| Barbarigo (…3 April) | Torelli (…3 April) | Bagnolini (…13 April) |
| Archimede (…15 April*) | Finzi (…18 April) | Da Vinci (…) |
Grand-Admiral Dönitz visited Bordeaux and Betasom on 22 April. Admiral Kratzenber also visited the base and boarded the submarines Cappellini, Tazzoli, and Giuliani to examine the work being carried out to transform them into transport submarines. The Italians asked Dönitz for type IXC U-boats for the exchange. Dönitz replied that they were available but suggested that type VIIC boats were more suitable for the Atlantic War.
On 5 April 1943, a Brazilian Air Force Hudson A-28 aircraft from Ibura Field, Recife, Pernambuco, piloted by Tenente Ivo Castaldoni, was sweeping the area behind convoy TC.9 when an object believed to be a submarine was sighted and attacked in 11°25’ S, 36°27’ W. It was not certain if Archimede went as far south as this; later, it was believed that the Brazilian had attacked the wreck of the Swedish Industria sunk by U-518 (KL Friedrich-Wilhelm Wissmann) on 25 March.
Loss of Archimede
On 15 April 1943, two PBY-5A Catalina aircraft of the 93rd Patrol Squadron (they belonged to the U.S. Navy Patrol and were part of VP-83) piloted by Ensign T.E. Robertson and Lt Gerard Bradford, Jr. sighted the Italian submarine Archimede (T.V. Guido Saccardo) and sank her. Despite the massive explosion captured by photographs, several crew members survived the attack. Twenty-seven days later, only one delirious survivor, Giuseppe Lo Cocco, reached the Island of Bailique (the western shore of the Amazon River), where he was rescued by Brazilian fishermen. The Brazilian gunboat Risiner brought him to Belem on 6 June. Nine officers and fifty-one ratings perished.
On 18 April, while following a Sperrbrecher on passage from Bordeaux to Pauillac, Finzi (T.V. Mario Rossetto) detonated a mine under her keel. It may have been laid by HMS Cachalot on 28 March 1941. Although these mines had flooders set for 27 April 1941, a rogue mine may have survived. However, it was most probably an air-laid mine. The submarine suffered some damage to her auxiliary motors.
Following a discussion the previous month, on 29 April, the BdU proposed the exchange of nine Type VIIC U-boats for the large Italian submarines based in Bordeaux. These would be used as transports to the Far East.
The following submarines were ear-marked:
| Submarine | Shipyard | Delivered on | Entry in service | Italian name |
| U-428 | Danzig | 30.06.1943 | 07.07.1943 | S.1 |
| U-746 | Schichau | 01.07.1943 | 08.07.1943 | S.2 |
| U-747 | Schichau | 15.07.1943 | 22.07.1943 | S.3 |
| U-429 | Danzig | 21.07.1943 | 28.07.1943 | S.4 |
| U-748 | Schichau | 05.08.1943 | 12.08.1943 | S.5 |
| U-430 | Danzig | 18.08.1943 | 25.08.1943 | S.6 |
| U-749 | Schichau | 19.08.1943 | 26.08.1943 | S.7 |
| U-1161 | Danzig | 08.09.1943 | 15.09.1943 | S.8 |
| U-750 | Schichau | 09.09.1943 | 16.09.1943 | S.9 |
In exchange, the Bordeaux submarines would be converted to transport materials. A tenth (U-1162, to be renamed S.10) would later be added in exchange for a Mediterranean-based submarine, but there is no evidence that the submarine ever flew the Italian flag.
Betasom assigned them code names ‘Aquila’ and the Germans ‘Mercator’.
| Enrico Tazzoli | Aquila I | |
| Reginaldo Giuliani | Aquila II | Mercator III |
| Comandante Cappellini | Aquila III | Mercator IV |
| Giuseppe Finzi | Aquila IV | Mercator I |
| Barbarigo | Aquila V | |
| Luigi Torelli | Aquila VI | Mercator V |
| Archimede | Aquila VII | |
| Leonardo da Vinci | Aquila VIII | |
| Alpino Bagnolini | Aquila IX | Mercator II |
| Ammiraglio Cagni | Aquila VIII (assigned after the loss of Da Vinci) |
The submarines Murena, Grongo, and Sparide were being built in Italy and equipped for special operations by the Decima Flottiglia MAS. Of the trio, Murena was to be assigned to the Atlantic Theatre, but the Armistice prevented the project from fruition.
Gamma men attempt at Huelva
The Decima Flottiglia MAS had created the Group G.O.G. using Gamma men based on the Italian merchant ship Gaeta (4,457 GRT, built 1927) anchored at Huelva (Spain) on similar lines to Olterra at Algeciras. British shipping used Huelva to load iron ore, and Italian Gamma swimmers Sottocapo Salvatore Nizzi and 2o Capo Carlo Vianello carried out several attacks on British shipping in the spring of 1943.
During the night of 22/23 April, they claimed to have attached explosive charges on a vessel of 4,500 GRT which was blown up the next day. This was not confirmed by British records, the target was probably the British steamer Camerata (4,875 GRT, built 1931), who had two limpets removed on 8 May.
Indian Ocean
Da Vinci (T.V. Gianfranco Gazzana Priaroggia) had now entered the Indian Ocean. On 17 April, she sank the Dutch Sembilan (6,566 or 6,633 GRT, built 1922) carrying ammunition and two landing craft (LCP–780 and LCP–782). Of the eighty-six passengers and crew, only one survived, the lascar Shamser who was near the stern section when the ship blew up and was thrown into the sea. He clung to a piece of wood and was found by the submarine and taken on board. He would later describe the submarine as “small” and that the submarine had a crew of about twenty-four, including four Italian officers and the remainder were German ratings. This shows how unreliable witnesses can sometimes be! The following day it was the turn of the British Manaar (8,007 GRT, built 1942) to be sent to the bottom by a combination of torpedoes and gunfire from the Italian submarine. Four men were killed, but ninety-four survivors, including the lascar from Sembilan, reached Port St. Johns (South Africa) in four boats. The Second Officer was taken prisoner by the submarine and would perish with her. On 21 April, it was the turn of the American John Drayton (7,177 GRT, built 1942). The survivors took to three lifeboats; the first, with eleven men, was found by the Swedish Oscar Gorthon, the second, with the Master and thirteen men, was found by the destroyer HMS Relentless whereas the third, with twenty-one men, was found only on 20 May by the Greek Mount Rhodope after twenty-nine days. By this time, only eight men were left alive, and three would succumb in hospital. On 25 April, Da Vinci used her last torpedoes to sink the British tanker Doryssa (8,078 GRT, built 1938). Fifty-three were killed, and eleven were rescued by the minesweeping whaler HMSAS Southern Barrier. But this was her last victim. On 30 April, the most successful Italian submarine sent her last signal.
