Length |
10 – 10.4 metres |
Wide |
1.9 metres |
Height |
1.6 – 1.8 metres |
Displacement |
12 – 16.4 tonnes |
Propulsion |
Isotta Fraschini diesel engine Brown Boveri electric motor |
Armour |
– |
Armament |
Torpedo Version
- 2 x 450 millimetres torpedoes
- 2 mines
Gamma Diver Transport Version
- 8 x 100 Kilogram explosives
- 20 Bug Limpet Mines
History |
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The first two CA-class assault submarines, designed and constructed by Caproni in Milan-Taliedo, are delivered to the Regia Marina in April 1938. Known as ‘Submarine Ambush Motorboats,’ they are designated CA 1 and CA 2 (short for ‘Caproni type A’). However, to maintain secrecy, they are not officially listed in the Navy’s records. Initially, the plan is to deploy a significant number of these submarines to form defensive barriers along key coastal areas, such as the gulfs of Genoa and Naples, the Tuscan and Dodecanese archipelagos, and various strategic channels. There is also consideration for their potential use in assaults on enemy bases.
Displacing approximately 13 tonnes on the surface, these submarines have a crew of two and carry two 450 millimetres torpedoes. Their compact dimensions, with a maximum length of 10 metres, allow for easy transportation by rail, much like the A and B types developed during the First World War. The two prototypes undergo extensive trials in Venice and La Spezia between 1938 and 1940. Although no major faults are identified, the vessels prove fragile and difficult to manoeuvre underwater. By 1939, a redesigned version, featuring significant modifications, including an additional crew member, is already in development.
This redesign leads to a further evolution of the concept, resulting in the construction of the CB-class pocket submarines, which boast greater displacement and improved performance. While their impact in the Mediterranean theatre is limited, they achieve notable success in the Black Sea, particularly during the siege of Sevastopol, where conditions are well-suited to their design.
The CA-class mini-submarines are completed in 1940 and, having fulfilled their experimental role, cease operations. The two vessels are left at the La Spezia submarine dock, neglected for some time. Following initial successes with assault craft, British defences in Mediterranean ports are significantly strengthened. Patrol boats continuously monitor harbour entrances, drop anti-personnel depth charges, and illuminate defensive nets and booms with searchlights. These enhanced defences claim the lives of several Siluro a Lenta Corsa operators. Even when physical damage is avoided, divers endure extreme strain, which, combined with the discomfort of their breathing apparatus, can limit their effectiveness.
Although the use of Gamma divers shows promise, their operational range and explosive capacity remain limited. Moreover, they are highly vulnerable to defensive measures. Commander Angelo Belloni, an innovator in underwater equipment, collaborates with Lieutenant Eugenio Wolk, leader of the Gamma diver unit within the Decima Flottiglia MAS, to develop a new type of underwater craft. This vessel is intended to transport multiple divers and their explosives, providing greater protection from depth charges. Smaller than a standard submarine, it would be less detectable by modern surveillance systems and could navigate into enemy harbours with relative ease. Once submerged near the target, the craft would allow divers to deploy explosives directly or conduct multiple underwater missions within the harbour.
Divers using this new craft would differ from standard Gamma operatives by spending the majority of their missions underwater. In contrast, Gamma divers rely on lightweight breathing apparatus and operate primarily at the surface, diving only when necessary. The new craft would shelter the divers during penetration of defensive barriers and facilitate underwater towing to reduce fatigue. After completing their mission, the divers would re-board the craft to escape the harbour.
Given the need to maintain a small, stealthy profile, the craft’s range and seaworthiness are necessarily limited. As a result, it requires an ‘approacher’ vessel to transport it near the target zone. This larger vessel, most likely a submarine, would release the craft once in proximity to enemy harbours and wait for its return.
In 1941, the Decima Flottiglia MAS requests access to CB-class submarines for trials off La Spezia. When this is denied, the two decommissioned CA-class submarines are reassigned for experimental use in September 1941. The vessels, having undergone years of trials, are worn but undergo refurbishment at Caproni’s Milan-Taliedo facility. By November 1941, CA 2 completes modifications, including the removal of its diesel engine, conning tower, and periscope. Its torpedoes are replaced with eight removable 10 kg depth charges. A new electric motor, combined with streamlined modifications, enhances underwater speed and range.
Trials are conducted at Lake Iseo from November 1941 to February 1942. Despite harsh winter conditions, tests yield satisfactory results, with the vessel achieving a dive depth of 47 metres. However, further modifications are necessary, including the addition of a diver lock-out chamber. CA 1 is transferred to Lake Iseo soon after, but an accident during maintenance delays testing until summer 1942.
Although trials indicate the craft meets operational expectations, they also reveal significant shortcomings, including poor depth control, noisy electric pumps, and cumbersome charge deployment. Hand-operated pumps replace the electric ones, but further refinements are required. A second series, designated CA 3 and CA 4, incorporates improvements such as enhanced structural strength, larger rudders, and bow diving planes.
Gamma Diver Assault Transport |
Recognising the unique attributes of the CA-class mini-submarines, the Italian Navy decides against deploying them immediately in the Mediterranean. The robust harbour defences in the region would likely thwart the imperfect craft during their initial missions, while the availability of proven Siluro a Lenta Corsa’s reduces the necessity for untested vessels. Instead, the Atlantic theatre is selected, where no previous assault craft missions have been conducted. By mid-1942, Mediterranean defences have evolved to such an extent that only experienced and tested craft can hope to succeed. The Atlantic offers a less fortified environment, allowing the CA to demonstrate its effectiveness without exposing it to excessive risk.
In 1942, trials on Lake Iseo see Commander Junio Valerio Borghese personally overseeing the conversion of CA 2 into a Gamma diver carrier. This innovative project, spearheaded by Decima Flottiglia MAS, shows considerable promise and later inspires significant post-war advancements in naval design. Unlike the Siluro a Lenta Corsa, which typically requires multiple units to achieve substantial damage, a single CA craft, with its array of explosive charges, possesses the potential to inflict severe damage on enemy bases. In contrast, during 1942, even the largest submarines used to transport Siluro a Lenta Corsa’s are limited to carrying three units at most.
Strategists believe that just one or two successful Atlantic operations involving CA 1 and CA 2 could severely disrupt Allied shipping and naval activities, forcing them to develop entirely new defensive strategies for ports previously deemed secure. The psychological and operational impact would likely divert substantial Allied manpower and resources towards defensive measures, detracting from other essential wartime operations.
Original plans propose two missions. The first involves transporting a CA aboard an Italian ocean-going submarine, while the second envisions a German U-boat, most likely a Type IX, carrying the second craft. However, when the Italian Navy approaches the German High Command to request a submarine and intelligence regarding Allied ports in the Atlantic, Africa, and the United States, they receive a lukewarm response. German Admiral Karl Dönitz, committed to the convoy war, declines to allocate any submarines, citing the ongoing demands of ocean warfare. Consequently, plans for the second mission are shelved, and the Italians resolve to proceed with a single CA transported by an Italian vessel. The Germans agree to share intelligence on Atlantic harbours but refrain from further involvement.
The operational plan necessitates transporting the CA aboard another submarine to the vicinity of the target harbour, where it would be released and later recovered. To explore the feasibility of this concept, trials are conducted to determine the practicalities of submarine-to-submarine transport. The Italian Navy opts to utilise one of its ocean-going submarines stationed at the Bordeaux-based Betasom facility, thereby avoiding the perilous passage through the Straits of Gibraltar.
In July 1942, CA 2 and its Decima Flottiglia MAS crew are dispatched by rail to Bordeaux. The Marconi-Class submarine Leonardo da Vinci, chosen over the Archimede due to superior speed, buoyancy, and range, undergoes conversion at the Betasom Submarine Workshop under Major Giulio Fenu’s supervision. By September 9th, 1942, the Leonardo da Vinci, with CA 2 secured on its deck, departs Bordeaux for Le Verdon, escorted by German naval forces for offshore trials.
Commanded by Lieutenant Gianfranco Gazzana Priaroggia, the Leonardo da Vinci conducts a dive to calibrate its trim before releasing the CA, operated by Sub-Lieutenant Eugenio Massano. After the CA is released, the Leonardo da Vinci surfaces and returns to Bordeaux, towing the mini-submarine. During the trial, CA 2 inadvertently collides with the submarine’s conning tower, causing minor damage but remaining operational.
A second trial on September 13th, 1942, encounters strong currents, resulting in further minor damage to the Leonardo da Vinci’s railings. Nevertheless, on September 15th, 1942, a successful release and recovery operation is executed. Subsequent tests refine the process, culminating in the nickname kangaroo for the Leonardo da Vinci, due to the CA’s snug fit on its deck.
The crew conducts additional trials to evaluate the submarine’s handling with the CA onboard, but rough seas near La Pallice result in further damage to the CA. By September 23rd, 1942, the Leonardo da Vinci returns to Bordeaux, ending the series of tests with satisfactory results. The CA is removed, and the Leonardo da Vinci resumes active patrol duties in the Atlantic.
Trials validate the feasibility of transporting and deploying the CA from larger submarines, reinforcing the potential of the craft for future operations. However, damage from rough conditions highlights the CA’s fragility. Additionally, mechanical failures during testing indicate that the craft remains prone to malfunction, underscoring its unsuitability for high-risk missions at that stage.
Due to incomplete intelligence on Atlantic targets, planned missions are postponed until enhanced versions of the CA (ordered from Caproni) are operational or until CA 1 and CA 2 achieve reliable performance. Development of CA 3 and CA 4 progresses slowly in Milan, reflecting adjustments informed by experience with the earlier prototypes. The newer models feature enhanced hull strength, improved hydrodynamics, and increased rudder and bow-plane control.
By January 1943, the Navy receives CA 3 and CA 4, transferring them to La Spezia for trials. Meanwhile, Decima Flottiglia MAS continues to refine operational plans, focusing on targets such as New York Harbour. One ambitious proposal involves transporting a CA to the mouth of the Hudson River, from where it would navigate upstream to target vessels docked in the harbour. The likelihood of the CA returning is minimal, with crew survival reliant on evasion or surrender.
Armatice |
By mid-1943, Italian strategists aim to launch these missions by the year’s end. However, logistical delays, training requirements, and ongoing mechanical issues push back the timeline. The Italian Armistice of September 8th, 1943 halts all CA operations. The Germans seize CA 1, CA 3, and CA 4 at La Spezia, while CA 2 remains in Bordeaux. Some sources suggest that one unit is transported to Germany for further evaluation, but no missions are conducted. Post-armistice, Decima Flottiglia MAS Commander Angelo Belloni attempts to revive training efforts, but the deteriorating war situation limits progress.
Ultimately, CA 2 is found unserviceable by Allied forces in Bordeaux and subsequently scrapped. Despite never engaging in combat, the CA-class concept influences post-war submarine development.
Multimedia |
CA-2 Trials on Lake Iseo |






Marconi-Class Submarine Leonardo Da Vinci (Modified) |



