Submarines Class Type C.R.D.A.

(Cantieri Riuniti dell’Adriatico)


The genesis of the ARGO class and its derivates, the three TRITONE classes, is unusual. While most of the submarine fleet already in service in the Italian Navy in the 30s and in later years was the result of a close collaboration between the Navy (well-known designers such as Bernardis and Cavallini) and the private industry, the class ARGO was the result of the independent design work of the C.R.D.A. shipyard of Monfalcone. The Italian shipbuilding industry produced several boats under foreign commission; one of these classes of submarines was the ARGO, a double hull boat of the Laurenti design. The ARGO class included two vessels, the ARGO and VELELLA, both ordered by the Portuguese Navy in the early 30s.

The ARGO in Cagliari (Sardinia) upon its return to the Mediterranean Sea from Bordeaux.
(Photo courtesy Erminio Bagnasco and Achille Rastelli)

Laid down in 1931, the submarines of the ARGO class were almost completed when the Portuguese government cancelled the order. Some sources attribute the cancellation to financial difficulties, but it appears that the project was abandoned due to the tension arisen between Rome and Lisbon over the Italian occupation of Ethiopia (1935). The builder, C.R.D.A. of Monfalcone, offered the boats to the Italian Navy which had been paying attention to the project all along, and after a delay, these submarines were eventually modified and accepted into the Regia Marina. Modifications involved the adoption of equipment and technical solutions already in use on other classes of submarines, thus facilitating the training of personnel and maintenance.

The resistant, or pressure hull of the ARGO. Note the steel plates were riveted to cylindrical beams, and how the hull decreased in diameter toward the ends.
(Photo Turrini)

The ARGO class was too large to be considered coastal and too small to be considered fully oceanic, still both the ARGO and VELELLA performed well during operations in the Atlantic Ocean. Thus, the ARGO and the later TRITONE classes should be considered medium displacement submarines.


Battery hold

deck gun

Electric motors

Diesel engines


Kitchen (galley)

Officers quarters


Radio room

Torpedo launchers

Design and Construction

Since the creation of the first submarines, and not until the introduction of more revolutionary designs later in WW II and in the post-war period, submarines were made up of three distinct components: inner hull, outer hull, and superstructure.
The ARGO class had two hulls. One, internal, was divided into three sections; one in the middle and perfectly cylindrical, and two at the extremities, cuneiform in shape and decreasing in diameter to the ends which were in the form of semispherical bulbs. The internal hull was made of steel with low nickel content and 14.5 mm in thickness (diminishing to 14 mm at the extremities). These steel plates were riveted to cylindrical beams (reinforcement rings) spaced between 520 mm and 550 mm. The plates were double riveted and positioned in a brick layer fashion (each plate tended to overlap the other half of the adjacent plates.

The external hull, 6 mm in thickness, enclosed the fuel and water tanks, asset tanks, and oil tanks. Internally, the submarine was divided into six compartments:

Aft torpedo room and electric motors room
Engine room
N.C.O.’s quarters and aft battery hold
Control room and auxiliary equipment room
Officer quarters and forward battery hold
Forward torpedo room

Light structures made up the bow and stern, aft and forward of the hull, giving the submarine a flat deck, a cruiser-like bow and a round stern. This part was usually completely open to the ocean and seawater drained through wide openings above the outer hull.


Diesel Engines

The ARGO class was equipped with two two-stroke reversible diesel engines FIAT Q 274R. Each engine, capable of 420 rpm, produced 600 HP, but could be pushed for short periods of time up to 460 rpm achieving 750 HP. The TRITONE, built several years after the ARGO, received a new engine, the FIAT MEX 328R, an 8-cylinder diesel engine capable of generating 1200 HP at 450 rpm.

The surface speed of the ARGO class was around 14 knots on the surface and 8 knots submerged. The TRITONE maintained the same submerged speed, while surface speed was increased to 16 knots. After intense use, the diesel engines were prone to failures and required extensive maintenance. The limited speed of the ARGO was not a great factor, but in bad weather the engines’ intake valve, situated just above the engines on the deck instead of inside the conning tower as in foreign design, would easily flood.

In general, as for most Italian submarines, the surface speed of all the ARGO and TRITONE was very limited and could not be improved with the installation of new engines. A German type VII A submarine, smaller than the ARGO, could reach 17 knots versus the 14 of the Italian boats.

Electric Motors

Both classes received electric motors produced by the C.R.D.A. Those installed on the ARGO produced 400 HP each (300 HP under normal conditions and 400 HP for brief periods of time). The ones installed on the TRITONE appear to have been similar in performance, but it is not sure if they were the same model.

These motors could operate at 45, 90 and 180 volts. The maximum output was obtained running 180 volts and 330 RPM. When not in use for propulsion, the electric motors could be used to generate D.C. (direct current) to recharge the batteries.

Transmission Shaft
Each diesel engine was connected “in line” with the corresponding electric motor via a gear joint. Another gear joint connected the electric motor to the propeller shaft. During normal diesel operation, the electric motor would rotate freely. During electric propulsion, the first joint was disconnected, thus freeing the diesel engine. During the recharging of the batteries, the second joint was disconnected, leaving the diesel engine to drive the electric motor at a fixed predetermined speed.


On both classes there were two holds capable of holding 52 batteries each. On the ARGO, each cell weighed about 750 kg each. The total weight of all cells was 78 tons. The batteries could deliver 4,750 amps in one hour, 7,050 amps in three (2,350 amps/hour), and 9,720 amps in twenty hours (485 amps/hour). These are performances identical to the ARGO and TRITONE class.

Each cell was made of multiple positive and negative plates made of lead, each with common terminals, separated by insulators. The plates were immersed in an electrolyte solution made of pure water (distilled water) and pure sulfuric acid with a specific gravity of around 1.25 when fully charged. Each cell produced approximately two volts and was permanently wired in series. Each of the two battery groups could be operated independently or in parallel. On the ARGO and TRITONE each battery group was divided into two busses, each composed of 26 cells (26 x 2 volts = 52 volts).

Air Systems

Compressed Air

The compressed air system was one of the most important systems on the submarine. It was used to blow the ballast tanks, fire torpedoes, and to start the main engines. Without a functional air system the submarine became inoperable. Docking facilities were usually provided with the necessary high-pressure air supply so that the submarine would not have to produce its own. Air tanks tended to accumulate condensed moisture (water), thus they were regularly drained for maintenance. On the ARGO and TRITONE class the primary air compressor was installed in the auxiliary room.

Additional information regarding the air system is limited, but we know that these boats were equipped with:

· High-pressure air compressor
· Turbo-blower: These compressors could only be used when the submarine had at least the conning tower out of the water so that the hatch could be open to supply external air.
· Trim pumps (50 tons per hour up to 120 meters)
· Bilge pumps (30 tons per hour up 120 meters)
· Manual pumps

Air Filtering System

The ARGO and TRITONE class were equipped with an air filtration system for the removal of CO2 (carbon monoxide). There were also oxygen tanks used to oxygenate the depleted air while submerged. The submarine was equipped with external hookups so that, in case of malfunction, a support ship could blow the ballast tank and also provide breathable air. Due to the primitive nature of the air circulation system, when submerged, the crew would experience very uncomfortable conditions and the air was reportedly foul within a very few minutes.

Crew Quarters

On the ARGO and TRITONE the officer quarters were located just forward of the control room and past the R.T. and hydrophone rooms. The captain had a private quarter separated from the square (officer quarters) by a curtain. The other three officers each had a private bunk. The non-commissioned officers shared the space aft of the control room, while the rest of the crew would use the temporary bunks in the forward and aft torpedo rooms.


On the ARGO there were two galleys, one powered by electricity and one burning diesel fuel located within the conning tower. Eventually, the galley located in the conning tower was found impractical and the TRITONE class had it removed. Meals at sea were very simple, and cooking underwater was discouraged due to the generation of water vapors which would eventually create further condensation.


There is no specific information available, but it should be assumed that these boats had at least two heads, while the early ARGO class had additional facilities located in the conning tower.
Fresh Water
The submarine had a small reserve of fresh water.


There was a small refrigeration system located in the auxiliary equipment room, quite far from the galley, which was located in the forward torpedo room. Non-perishable food was instead stowed in a small hold situated in the forward torpedo room.


The ARGO had a crew of 4 officers, 10 non-commissioned officers and 26 leading and enlisted men. The four officers were the commanding officer, usually a T.V., his second, the chief engineer and another engineer.

Safety Systems

The ARGO and TRITONE class were not equipped with the expensive Gerolami-Arata lifts, a device consisting of a sealed chamber which would float to the surface by buoyancy and could then be retrieved by a tether connected to the bottom of it and secured to a winch. There were external hook ups to connect a sunken boat to external air and water lines. Also, each boat had two floating buoys installed above each torpedo room and which could be released to the surface. Each buoy was equipped with a telephone system and devices to have them easily located.

Communication, Radio, and Navigational Systems

The radio room was installed forward of the control room in a dedicated cabin. There were multiple radio apparatuses: a radio transmitter (300 to 2,500 meters), a radio receiver (300 to 10,000 meters), a short-wave radio transmitter capable of 400 watts (15 to 60 meters) and a receiver for the same frequencies.

General announcing system

All ARGO and TRITONE were equipped with an announcing system. Each compartment could communicate with a central station located in the control room via a speaker microphone system. The internal telephone system had only four stations.

Alarm system

As already said, the ARGO and TRITONE were equipped with a klaxon operated from the control room. Upon sounding the alarm, all hatches would be secured and the engineers would commence the diving procedures, securing the diesel engines’ intake and exhaust valves.

Telephone call system

These submarines were equipped with two buoys situated on deck and attached to a retrieval system. If necessary, the buoys could be released and floated to the surface, giving surface units a telephone connection to the submarine.


There was a hydrophone system connected to external transmitters. The system was of domestic production and considered effective.


The ARGO and TRITONE classes were equipped with a gyrocompass installed in the auxiliary room which had three repeaters installed in various compartments (and also in the wheelhouse). There was also a magnetic compass installed in a waterproof casing on deck with a repeating station in the control room.

The gyrocompass received its directive from a high-speed spinning gyroscope driven by electric motors. Its directive action is based on the mechanical laws governing the dynamics of rotating bodies. When any object is spinning rapidly it tends to keep its axis pointed in the same direction. The gyrocompass consists of a spinning gyroscope, made north seeking by placing a weight below the axis, which is mounted in gimbals so that the movements of the submarine do not effect its position. A dial mechanically connected to the gyrocompass has the points of the mariner’s compass marked on it and indicates the submarine’s true course. The gyroscope required some time before becoming operational, thus it had to be started in advance of leaving port.


There were two periscopes. The forward one, used to attack, was produced by San Giorgio, while the aft one, used for exploration, was produced by the firm Galileo. Typical of Italian submarines, the periscope sleeves extended considerably from the conning tower and were enclosed in a light metal structure quite visible from a distance. On the TRITONE the periscopes reflected the German style conning tower and were completely recessed. Both the exploration and attack periscopes were accessed from the control room and their wells went down all the way to the keel.


When the ARGO and TRITONE were on the surface, they operated like any other boat demonstrating good seaworthiness. Maintaining the various ballast tanks full of air provided buoyancy.


The rudder (semi-compensated) was controlled electrically from the control room, or manually for the aft torpedo room. Also, there was a wheel in the conning tower in an enclosed wheelhouse.

Diving Planes

As standard on most submarines, the ARGO and TRITONE were equipped with two sets of diving planes. The forward planes were collapsible (folded upward) for surface navigation and were placed above the waterline. The aft planes were fixed and placed below the waterline in line with the two propellers. The forward planes were used to control depth, while the aft ones were used to control the angle of the boat. The planes were controlled electrically from the control room, but could also be manually operated from the torpedo rooms.

The ARGO and TRITONE were equipped with a primary anchor, installed on the port side, and the chain was stored in a well located below the forward torpedo room.



All ARGO and TRITONE were fitted with two torpedo tubes aft and four forward. All tubes were loaded before leaving port and six extra torpedoes were stowed aboard giving the ARGO and TRITONE a total of 12 torpedoes. Torpedoes were loaded through a special hatch and the operation was very laborious. Once at sea, torpedoes could be removed from the tubes for limited maintenance (fuel topping).

Range, speed and direction of the weapons could be configured while they were inserted in the tubes. The tubes, produced by Tosi, could take a variety of 21’ (533 mm) torpedoes produced both by Whitehead and “Silurificio Italiano”. Similar to the Royal Navy, the Regia Marina did not experience the kind of massive torpedo failure which plagued the U.S. Navy and the Kriegsmarine. Italian weapons were reliable, but left a visible trail thus making them easy to spot. Toward the end of the war (1943), the TRITONE received electric torpedoes from the Germans which proved quite effective.

Smaller Weapons
Each boat was equipped with a small armory containing rifles and side arms and located in the hydrophone room.

Deck Guns

The ARGO and TRITONE were fitted with the newer 100 mm caliber 47, and carried 149 shells. A well-trained gunnery team could fire eight shells per minute.

100-47 O.T.O. 1938

The ARGO and TRITONE had a single gun mounted forward of the conning tower. Shells were loaded from the stowage area below onto the main compartment and from there pushed up to the deck through a tube. Since there are no specifications for a mechanical or hydraulic hoisting system, it is assumed that the shells were pushed by hand. The gunners also had access to a ready storage area built into the conning tower and secured by a watertight hatch. The ammunition stowage was located on the lower deck between the forward battery hold and the quick dive tank.

Due to the nature of the conflict in the Mediterranean, the deck gun of the ARGO and TRITONE was of very limited use.

Machine Guns

All ARGO and TRITONE classes were equipped with the famous Breda Model 1931 13.2 mm anti-aircraft machinegun. These guns were mounted on a single support on the ARGO and on double mounts on the TRITONE. The guns were installed on a retractable mount, which would recede into a watertight tube protected by a small hatch.

Breda Model 1931 13.2 mm anti-aircraft machinegun

Upon emerging, the gunners had to simply release the hatch, lift the guns out of the enclosure, and install the clip and fire. Each clip contained 30 rounds and the gun could fire up to 400 rounds per minute at a range of 2,000 meters. The ARGO had a reserve of 3,000 rounds, later increased to 10,000 on the TRITONE. As with all Italian submarines, toward the end of the conflict it was discovered that the 13.2 mm guns were insufficient in downing large American bombers protected by a thick armor.