Monday, September 6, 2010

Yugoslavia's Sabotage Submarines

Croatian Navy (HRM) P-01 Velebit, formerly P-914 Soca
Small submarine operations in the former Yugoslav Navy (JRM) were a part of the SFRY’s (Tito’s Yugoslavia, the Socialist Federal Republic of Yugoslavia) defensive partisan warfare doctrine, which was intended to deter both the west and the Warsaw Pact from invading, and failing deterrence, to combat one or both opponents using partisan and guerrilla tactics. Following the collapse of the SFRY, the FRY consisting of Serbia and Montenegro carried this doctrine forward in the RMVJ (Navy of the Yugoslav Army, the SFRY’s naval force).  Under the doctrine of “Total National Defense,” the conventional submarine force constituted part of the country’s initial line of defenses, while the midget submarines, known as “sabotage submarines” in Yugoslav terminology performed a diversionary role, laying offensive and defensive minefields, striking enemy forces in port, and at anchored invasion forces once a beachhead had been established. A discussion of Yugoslav defensive naval doctrine will form the basis of a separate post. 
P-916 Vrbas

Although the JRM had experience operating a former Italian CB-class midget submarine in the 1950s, the requirement to build a small “sabotage” submarine was only established in 1977.  During the early 70's, while the B-71 and B-72 (Heroj and the Sava) programs still were still underway, development of small submarines suitable for operation in the area of about two-thirds of the surface of the Adriatic Sea north of a line from Molat Island to Ancona in depths of less than 150 meters was discussed. Operation of large submarines  along the coastal shelf on the Italian side of the Adriatic, some 10-20 nm wide, with depths of less than 20 meters was out of the question. Operations there would necessitate development of midget submarines for the JRM.
P-912 Una in the Tivat Repair Arsenal, ca. 2008

The first preliminary analysis of a small torpedo-attack submarine type M-100 and a small sabotage submarine-type M-40 was conducted in 1974. This studied a requirement for a submarine that could transport, disembark and re-embark underwater demolitions teams and their equipment, lay offensive and defensive minefields, have the capability of carrying two torpedoes, and collect tactical intelligence. While larger submarines could be and were used for such operations in the JRM, operational experience pointed out the greater suitability for small or midget submarines in this role, which led to the establishment of a 100-ton upper limit for design displacement, and gave the class its designation of “M-100.” It should also be pointed out that the term “sabotage submarine” did not imply “submarine sabotage,” which in the Yugoslav context meant “saboteurs” inserted individually or as a team into the immediate area of operations upon exit from the submarine, and which more normally implied “wet” submarines, i.e., swimmer delivery vehicles such as the R-1 and R-2. 

Design specification requirements included:

  • Shallow water (10-15 meters) maneuvering capability

  • Maximum diving depth 150 meters at a 4kt speed, with 80% battery expenditure

  • Working depth of 90 meters

  • Good habitability sufficient for 48 hours autonomy

  • Maximum underwater speed of 6-7kts

  • Good controllability and maneuverability at speed of only 1kt
 Tests conducted on P-911 indicated the design met all requirements, with the overall class technical specifications resulting as follows: 
Length: 19.52 m
Width: 3.64 m
Diameter: 2.70 m
Height to deck superstructure: 3. 38 m
Height to periscope:  5.30 m
Displacement, surface:  79.58 t
Displacement underwater:  90.27 t
Reserve Buoyancy: 10-14%
Operational Diving Depth: 105 m
Maximum depth: 120 m
Computational depth: 181 m
Minimum depth of the sea for diving: 10 m
Underwater speed, max:  7.48 knots
Underwater speed, economical:  4 knots
Surface speed:  5.9 knots

Range of navigation with 80% of Battery Expenditure:
at  6.4 knots and external attachments (R-1, etc) : 106 nm 
at  4 knots and clean hull: 254 nm
at  5.9 knots on the surface: 90 nm
Total range with 100% expenditure battery at 3 knots: 270 nm

with full crew (6 people): 160 hours
for 10 people (4 crew and 6 div.): 96 hours

Sabotage resources:
2x R-1 vehicles mounted forward under casing hatch
2x R-1 vehicles mounted aft under casing hatch
Div. mines, M 66 or M 71: 6 or 12 pieces.

Mines:  AIM - M 70 or AIM - M 70/1: 4 pcs.
Pistols: 4 pcs.
flare guns: 1 pc.

The M-100s were assigned to the 88th Submarine Brigade, but supported the 82nd Maritime Center, stationed at Kumbor in Boka Kotorska, Montenegro. In operational practice, they proved to be an extremely quiet and likely very effective design. Yugoslav sources claim that no M-100 was ever detected during an operation, nor even on a “friendly” training exercise with JRM forces. During initial testing, P-911 repeatedly crossed the hydrophone line at the entrance to Lora inlet, where the main JRM base was located at Pula. At no time was the boat detected by the hydrophone array. It is also reported that while conducting a patrol 30 nautical miles out from the Montenegrin coast just before the Allied bombing campaign of 1999, P-913 encountered a NATO submarine. Remaining behind at a distance of 100 meters, the “uninvited guest” reportedly failed to detect the midget. If this incident is true, and we have no reason to doubt its author, this represented a significant vulnerability on NATO’s part, or a significant strength on the part of the RMVJ, depending on one’s point of view. 
P-914 Soca launch

As built, the M-100s were powered solely by batteries with no on-board recharging capability. P-914, which had been left behind in Split upon Croatia's secession from Yugoslavia, was rebuilt and lengthened approximately one meter to incorporate a diesel generator. P-914 was renamed Velebit (P-01) upon recommissioning into the Croatian Navy, serving until 2006. Some confusion among outside observers has arisen concerning the presence or absence of sails/conning towers on these boats. Local writers comment that these "sails" are actually removable plastic units, which serve as crew protection, and were most often used only in port. The exception to this is Velebit, which after its modifications, appears to have retained the sail permanently. As a class, the M-100s have fared well, with all but one surviving the scrapper's torch, being donated to museums around the former Yugoslavia. 
RMVJ units on parade in Boka Kotorska, mid to late-1990s
 Fates of the P-911s are shown below:
BSO =  Brodogradiliste Shipyard, Split


Thursday, September 2, 2010

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

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 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

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
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


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.

1x Cummins diesel-electric, 300hp
1x 75hp engine generator
Battery: 24V 1100 Amp
1x screw

Surface: 75 tons
Submerged: 90 tons
Autonomy: 20 days
Dimensions (2010):
Length: 23 meters
Beam: 2.2 meters
Height: 4 meters

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