Italian Small Submarines

(Work in Progress, to be continued)

Since before the Second World War, Italy has been a prolific designer and producer of small submarines. The CA and CB-class midget submarines and their operational histories are already well-known, but those produced post-WWII are much less known, poorly documented and the subjects of confusion and misinformation. Fincantieri, Maritalia and Cos.Mo.S. are all known to have produced viable small submarine designs, however only Cos.Mo.S. is known to have definitely produced actual small submarines, albeit all for export.

This file is intended to serve as a repository for actual and projected post-World War 2 Italian small submarines designs. As always, comments and additional information are welcomed.

Cos.Mo.S. SpA, Livorno

Overview

Over the course of its 48-year history from 1955 to 2003, Cos.Mo.S. is believed to have produced a total of 24 midget submarines. Of these, 20 were delivered to five export customers, three were sold to Iraq but never delivered, and one remained at the Cos.Mo.S. factory as a demonstrator and developmental testbed. For further information on Cos.Mos.S. history, see separate entry under Italian Chariots.

Because of Cos.Mo.S' very secretive business practices, it may never be possible to completely ascertain all their boats' deliveries, but the most likely breakdown of their actual midget submarine deliveries is as follows (Provisional):

Type Date Quantity Customer

SX-404 1969 2 Taiwan

SX-404/B 1972 6 Pakistan

SX-506 1973 2 Colombia

SX-506 198? 2 Republic of Korea (i.e. South)

SX-756/K 198? 5 Republic of Korea

SX-756/W 1985 3 Pakistan

SX-756/W 1989 2 Iraq (never delivered)

SX-756/S 1989 1 Iraq (never delivered)

MG-120/ER unknown 1 Demo boat retained at factory

Cos.Mo.S' midget submarine designs were an ongoing evolution and expansion of essentially the same design over the course of 45 years from the mid-1960s to the company's demise in 2003. The company frequently marketed the same design under different designations to multiple potential clients. The reason for this practice is not known; possibly it was intended to reduce the possibility of clients becoming aware of each others' capabilities and Cos.Mo.S' relationship with them, or possibly it was simply to create the impression that Cos.Mo.S produced and sold more units than was actually the case.

(click to enlarge)

SX-404

SX-404 was Cos.Mo.S’ first known venture into midget submarine design and production. This was a 40-ton boat intended to transport naval SOF operators into hostile waters over distances greater than those that could be achieved by the company’s Chariot swimmer delivery vehicles (SDVs). All Cos.Mo.S’ midget submarines were designed with the capability of carrying two of the company’s CE2F-series SDVs.

Cos.Mo.S built two subvariants of this design, the SX-404, two examples of which were delivered to Taiwan, and the SX-404/B, six of which were delivered to Pakistan. The two subtypes are easily distinguished from each other by the presence or absence of a large horseshoe step on the sail. Pakistan’s SX-404/Bs have this step, Taiwan’s do not.

Displacement: 40 tons

Length: 59.1 feet

Width: 6.5 feet

Draft: 8.4 to 10.4 feet

Surface Speed: 10kts (designed), actual 4kts

Submerged: 7.2 kts

Max depth: 131.2 feet

Range: 1235 nautical miles

Crew 4 Officers, 2 NCOs, 6 passengers

Payload: 2 SDVs (CE2F Chariots)

SX-404 (above) and SX-404/B (below), showing evolutionary changes between the two sub-types

SX-404

Taiwan

Taiwan was Cos.Mo.S’ first midget submarine customer, taking delivery of two in 1969. As originally delivered, Taiwan’s boats had rounded bows, which were later modified to the more common ship-type bow seen on most other of Cos.Mo.S’ boats. The two boats, S-1 and S-2 served until 1973. Both boats are preserved and are on public display at the Taiwan Naval Academy.

Taiwanese SX-404, original configuration

Taiwanese SX-404, final configuration

source: Cos.Mo.S. SpA

SX-404/B

Pakistan

In the late 1960s, Pakistan ordered six SX-404s to a slightly modified design. The Pakistani Navy deployed its six boats against the Indian Navy during the 1971 war. One of them, reportedly fitted with external torpedo tubes fired on an Indian naval frigate, INS Kukri, but the torpedo remained stuck in its external launcher. Of the six, one was lost with all hands as a result of an accident on December 27, 1976. Following removal from service, four were scrapped and one was placed ashore as an exhibit in the Pakistan Maritime Museum in Karachi.

Pakistani SX-404/B on display at Pakistan Maritime Museum, Karachi

source: internet

SX-506

Colombia's two SX-506s in port, Cartagena, Colombia, November 2009

source: authors

S20 ARC Intrepido

S21 ARC Indomable

1972 - 07 August: Arrival in Colombia

1973 - 17 April Intrepido commissioned

1973 - 03 July Indomable commissioned

1980 - both modernized, lengthend 6ft to accommodate air conditioning unit

1995 - batteries replaced; auxiliary systems updated to incorporate automatic load control

1998 - 1st participation in annual UNITAS exercises

2003 - steel plating on outer hull casings replaced with anticorrosive steel at COTECMAR

Missions: shallow-water operations, commando operations, tactical amphibious reconnaissance, underwater demolition, attacks on port facilities, offshore installations, anchored or moored targets, beach surveys and intelligence missions.

Propulsion:

1x Cummins diesel-electric, 300hp

1x 75hp engine generator

Battery: 24V 1100 Amp

1x screw

Displacement

Surface: 75 tons

Submerged: 90 tons

Autonomy: 20 days

Dimensions (2010):

Length: 23 meters

Beam: 2.2 meters

Height: 4 meters

Armament:

8x explosive charges from 50kg to 2050kg, including the charges onboard chariots.

Mines: 6x Mk-21; 8x Mk-50.

Other Equipment:

2x CE2F/X-60 Chariots capable of carrying 8 submarine commandos and explosive charges.

Note: SX-506s are almost indistinguishable externally from SX-756s. The two Colombian boats can be distinguised from one another when their snorkel masts are raised. The ball mechanism on top of Intrepido's mast is flattened, whereas Indomable's is spherical. Both are distinguishable from South Korea's SX-506s by the step mounted around the sail, which is absent on the Korean units. Colombia's SX-506s are sometimes referred to as SX-506/B as a result of their lengthening, however this designation is not used by the Colombians, who usually refer to them as "Submarinos Tacticos."

One of South Korea's two SX-506s prior to delivery

source: Cos.Mo.S SpA