Saturday, May 28, 2011

Weekend Warships 3: Submarines - is the old becoming new again?

We're all familiar with submarines intended to fire torpedoes from underwater, as most of them have done since this type of ship became technologically feasible. However, from time to time designers and strategists have thought of other uses for submarines, making them more akin to surface vessels in some respects. In this Weekend Warships article, we'll examine some of those ideas, and see how the wheel may have just turned full circle.


Immediately before World War I, the Royal Navy decided it wanted to build a class of submarines fast enough to keep up with the battle fleet. They were to have a sufficiently powerful gun armament to duke it out on the surface with enemy merchant ships and smaller warships, as well as employ torpedoes for submerged combat.

The result was the 2,500-ton (submerged displacement) 'K' class submarine, with four bow torpedo tubes, four on the beam, and three cannon.

HM Submarine K6 (click the image for a larger view)

The 'K' class subs were steam-driven, to give them the necessary speed to keep up with surface combatants. This caused immense difficulties when trying to dive. The boilers had to be shut down, and the funnels and air intakes lowered and sealed, before the ship could submerge. It was claimed (with tongue doubtless firmly in cheek) that after their captains had given the order to submerge, they had time to walk around the deck and smoke a cigarette before going down the hatch! It routinely took as long as five minutes for these ships to submerge, with the record being held by K8 at 3 minutes 25 seconds. Normal submarines could submerge in less than a minute, so the 'K' class was very vulnerable to being shelled (by other ships) or bombed (by aircraft or airships) before they could hide beneath the waves.

HM Submarine K4 aground on Walney Island in January 1917.
Note how her hull is a hybrid design, incorporating both ship and submarine features.

The class was spectacularly dangerous to its crews, and equally unsuccessful operationally. Of the 18 built, six were lost in collisions and accidents (killing over 200 of their crews), but none to enemy action. Only one ever engaged an enemy vessel. It did so while submerged, and its torpedo malfunctioned, causing no damage.

The last four 'K' class submarines were heavily modified into the 'M' class, of which three were completed and the last scrapped. They were armed with a 12-inch cannon taken from old Formidable class battleships, a 3-inch gun, and four torpedo tubes. Amazingly, their big guns could be elevated to put the muzzle above water, so they could be fired from periscope depth!

HM Submarine M1

They were intended to serve as coastal monitors, but as far as is known, they never saw action. After the war, their 12-inch cannon had to be removed, because they contravened the provisions of the 1922 Washington Naval Treaty. One, M2, was converted to a submersible aircraft-carrier. We'll hear more about her later.

Germany also tried to build submarine 'cruisers'. She first constructed the large private 'merchant submarine' Deutschland , in an attempt to trade with the United States through the British naval blockade of Europe. This was successful, albeit to a very limited extent due to the small cargo capacity of such submarines.

German cargo submarine Deutschland in Baltimore harbor, July 1916

Later, Deutschland was militarized and renamed U-155. Its design became the basis for the U-151 class, of which seven were built. U-156, a member of the class, is shown below.

They were further developed into the 'Project 46' or U-139 class (3 built), displacing more than 2,000 tons. Below is a wartime photograph of an unidentified U-139 class submarine.

Both classes were armed with two 5.9" cannon, allowing them to stand off out of effective range of merchant ships (which by then were armed for self-defense with smaller cannon), and sink them at little risk to themselves. Later 'Project 46a' and 'Project 47' submarines would have been even larger and more advanced; but the war ended before the latter projects could become reality.

The German 'cruiser' submarines were not intended to operate with friendly surface ships, but rather to use their high surface speed to chase enemy vessels. Their large size gave them greater storage capacity for fuel and consumables, extending their range and operational endurance. Their heavy cannon were particularly important when confronting a Q-ship or 'mystery ship' - an innocent-seeming commercial vessel that was heavily armed with concealed cannon and depth-charges. Q-ships would try to lull U-boats into a false sense of security, so that they would surface and try to destroy their 'target' by gunfire instead of wasting a valuable torpedo on it. When they showed themselves, the Q-ship would unmask its batteries, hoist the battle flag, and open fire. As Commander (later Vice-Admiral) Gordon Campbell, a famous Q-ship skipper, wrote:

"... as [ships'] defensive guns increased in size so the submarine guns increased, and the large submarine which came out at the end of the war with their two 5.9 inch guns [i.e. the U-151 and U-139 classes referred to above] were a very serious problem. Had they come out earlier, defensively armed ships and mystery ships would have required 6-inch guns."

(Campbell, "My Mystery Ships", Chapter 2)

Britain's final attempt at a submarine with surface-ship-like armament and capabilities was HM Submarine X1, completed in 1925. It incorporated lessons learned from the German 'cruiser submarine' designs, as well as the British 'K' and 'M' class vessels.

X1 was the largest submarine in the world at the time of her launch, displacing 3,700 tons submerged. She was armed with four 5.2" cannon in two twin turrets, and six torpedo tubes.

She was never successful in Fleet service, breaking down frequently and proving very unreliable. She was placed in reserve after only a few years, before being scrapped in 1936.

The last attempt to produce a 'big-gun' submarine was the French Surcouf, classified as an 'undersea cruiser'. She was commissioned in 1934.

Surcouf (click the image for a larger view)

She was the largest submarine built prior to World War II, displacing almost 4,400 tons submerged. She carried a Besson MB.411 floatplane in a sealed hangar for aerial observation and gunnery spotting, and was armed with two Model 1924 8" cannon in a large watertight turret (the same weapons carried by the Duquesne and Suffren class cruisers, although the larger surface ships carried more of them).

Surcouf's 8" cannon. Note the muzzle sealing devices for underwater travel.

She also carried two 37mm. anti-aircraft guns and four machine-guns, as well as 10 torpedo tubes.

Surcouf had a checkered and largely unsatisfactory career. She was slow to dive and proved to be an unstable gun platform in heavy seas. Furthermore, she required a crew of well over 100, three times more than a conventional submarine.

When the Germans took over France in 1940, Surcouf was undergoing repairs in Brest. She managed to get across the English Channel to Britain, where she was taken over by the Royal Navy. After completing her interrupted repairs, she was handed over to the Free French Naval Forces. She escorted trans-Atlantic convoys until April 1941, when she was damaged during a German air raid on Devonport. She went to the USA for further repairs, and was then used by the Free French (without authorization from Britain or the USA) to occupy the Vichy French islands of Saint Pierre and Miquelon. This provoked real anger in the USA, but the occupation was eventually allowed to stand.

When war broke out with Japan in December 1941, Surcouf was ordered to Australia. She was en route from Bermuda to the Panama Canal in February 1942 when she was run down and sunk by an American freighter, with the loss of her entire crew. It was a tragic end to a troubled career.

There were a number of common threads running through all these submarine designs:

  1. They were fitted with a relatively powerful gun armament, allowing them to engage on the surface, as well as with torpedoes from underwater;
  2. They had a relatively high speed on the surface, to allow them to chase enemy ships and/or keep up with the surface vessels of their own fleet;
  3. They were considerably larger than 'normal' submarines of their day, permitting them to carry enough fuel and supplies to operate for extended periods at great distances from their bases.

However, the limitations of the technology of the day meant that none of these submarines was truly successful. They were 'hybrid' designs, trying to be 'all things to all men', combining two very different missions (surface and sub-surface warfare), and attempting to operate in two very different environments. The combination didn't work very well.


'Big gun' submarines weren't the only attempts to make a submarine more than just an underwater opponent. The concept of aircraft operating from submarines also dates back to the First World War, and this time the initial impetus came from Germany. In January 1915 submarine U-12 sailed from Zeebrugge in Belgium with a Friedrichshafen FF.29 floatplane secured transversely across its forward deck. A photograph of the occasion is shown below (with apologies for the poor image quality).

The submarine encountered heavy swells once outside the harbor. Fearing damage to the floatplane, the submarine's commanding officer, Kapitänleutnant Walther Forstmann, ordered it launched at once. He did so by simply flooding the submarine's forward ballast tanks, so that the boat's foredeck submerged beneath the plane. It floated clear, and its pilot, Oberleutnant zur See (later Vice-Admiral) Lothar von Arnauld de la Perière (who was to go on to become the most successful submarine commander in history), was able to take off from the surface of the sea, reconnoitering the coast of England before returning to Zeebrugge. Thus, although it wasn't carried more than a few hundred yards by the submarine, the concept of carrying an aircraft on the deck of a submarine had been demonstrated.

The British weren't slow to learn from this, particularly given the need to intercept Zeppelin air raiders. HM Submarine E22 was ordered to find out whether seaplanes could be launched from her foredeck.

'E' class submarine

She experimented with carrying two Sopwith Schneider (two-seat) or Baby (single-seat) floatplanes on her foredeck, launching them to intercept Zeppelins as they approached the English coast.

Sopwith Schneider floatplane

The tests were successful, but were not further developed for operational use, because in rough seas the planes would break free from the deck and be destroyed. Also, of course, the submarine could not submerge to avoid an enemy attack without losing its aircraft.

Germany tried to overcome this problem late in the war by designing a collapsible floatplane, which could be carried in a watertight compartment on the deck of its U-151 and U-139 class 'cruiser submarines' (mentioned above). It would be rapidly reassembled and launched to act as a 'spotter' for its mother ship. However, the end of the war terminated the program before a single aircraft could be embarked. After the war, the concept would reach its final form as the Caspar U-1 , which would inspire further developments in both the USA and Japan (of which more later).

Caspar U-1

Shortly after World War I, the US Navy obtained two Caspar U-1 aircraft from Germany. These were not considered satisfactory, but inspired further experiments with small collapsible floatplanes aboard the new 'S' class submarines. The lead ship of the class, S-1, was selected to conduct the experiments in 1923.


Wikipedia reports:

She was altered by having a steel capsule mounted abaft the conning tower; a cylindrical pod which could house a small collapsible seaplane, the Martin MS-1.

Seaplane pod aboard USS S-1 (click the image for a larger view)

After surfacing, this plane could be rolled out, quickly assembled, and launched by ballasting the sub until the deck was awash.

Martin MS-1 approaching USS S-1

These experiments were carried out into 1926 using the Martin-built plane, constructed of wood and fabric;

Martin MS-1 aboard USS S-1

and the all-metal Cox-Klemin versions, XS-1 and XS-2.

Cox-Klemin XS-2 aboard USS S-1 reports on the tests:

The Navy accepted delivery of 12 additional submarine-based aircraft and, although built by two manufacturers, the design was the same. Six were constructed by the Cox-Klemin Aircraft Corporation of New York and were made of wood and fabric. The other six were manufactured by the Glenn Martin Aircraft Corporation of Baltimore and were largely made of metal. This enabled the Navy to compare the new techniques using metal rather than wood.

During October and November of 1923, tests with the Glenn Martin MS-1 were carried out aboard USS S-1.

The S-1 had a complement of aircraft specialists from USS Langley aboard. Their duty was to erect and dismantle the aircraft and stow it away in the pressure-resistant tank aft of the conning tower. Unfortunately, it took nearly four hours to assemble the aircraft. This obviously was unacceptable and so modifications had to be made to cut down the assembly time. The modifications were carried out by the Naval Aircraft Factory at Philadelphia and, although the aircraft was delivered to them late in 1923, it was nearly two years before the modifications were completed.

In the summer of 1926, the complete cycle of assembly, launching, recovery and stowage of the modified Cox-Klemin XS-1, now designated XS-2, was assigned to the S-1. By the end of October, the launching crew had become so proficient with the modified aircraft that they could have the machine assembled, launched, afloat and with engine turning in 12 minutes. It took them only 13 minutes to recover, dismantle and stowaway, which was a truly remarkable feat when compared with four hours on the original aircraft. The XS-2 had an effective scouting radius of approximately 130 miles.

However, the experiments did not lead to the introduction of such aircraft into service aboard US submarines.

Britain tried to develop an aircraft-carrying submarine by modifying one of its large 'M' class vessels, which we discussed earlier. HM Submarine M2's gun turret was replaced by an aircraft hangar. Here she is shown extracting her aircraft, a Parnall Peto biplane, from its hangar, and launching it from her catapult. Click the pictures for a larger image.

Here's a contemporary video clip of how it worked.

The concept proved workable in calm seas, but less so in heavy swells. M2 was lost with all hands in January 1932 during an exercise. It was surmised that her aircraft hangar had flooded, causing her to sink.

The Italian Navy began work on a similar concept, commissioning the 'cruiser submarine' Ettore Fieramosca in 1930.

Ettore Fieramosca

She was originally built with a watertight hangar designed to accommodate a Macchi M.53 or Piaggio P.8 floatplane. However, the aircraft programs were canceled and the hangar removed before the submarine was finally handed over to the Italian Navy in 1931. She was immobilized by a battery explosion in 1940, and saw no further action until she was scrapped after World War II.

We mentioned the French submarine Surcouf earlier, in the context of her 8" gun turret. She also carried a floatplane for reconnaissance, a Besson MB.411, shown below taking off from the water.

Surcouf would hoist the plane out of the water using a crane, and suspend the fuselage from it to mount or remove the wings, floats, etc.

The aircraft was stored in a watertight hangar behind the conning tower.

Only two of these aircraft were built. One served aboard the Surcouf, the other with a shore squadron. Neither the submarine nor the aircraft survived World War II.

It was Japan which invested the most time, resources and energy into perfecting the use of aircraft aboard submarines. This is hardly surprising, given that she was faced with the vast expanses of the Pacific Ocean, and needed to be able to investigate very large areas at high speed, for fear that enemy ships might evade detection. It's more surprising that the United States, facing the same challenge, didn't do likewise with its own submarines.

Japan drew on both German and British experiments for her first submarine-launched aircraft. She obtained seven U-boats from Germany at the end of World War I as 'prizes of war', as she'd been on the Allied side during that conflict. Information gleaned from them (and imparted by German designers and engineers hired for the purpose) influenced Japanese submarine design in the 1920's. As she began building larger submarines in the 1930's, she borrowed heavily from the design of U-142, a large 'cruiser' U-boat (a development of the U-139 class mentioned above) that was completed just in time for the end of the war. It never saw action, and was scrapped soon after hostilities ended.

Japan began her investigation of aircraft aboard submarines by duplicating some of the experiments conducted by Britain, with E-22, and the USA, with S-1. She obtained two Caspar U-1 aircraft from Germany in 1921, which (as noted above) had been designed to be disassembled and stowed in a deck-mounted container aboard a submarine. Japan went on to build an indigenous version of this aircraft, the Yokosuka Navy 1-go, with a more powerful rotary engine.

This is the only photograph of the Yokosuka Navy 1-go known to exist

In 1927 submarine I-21 was assigned to conduct tests with the Yokosuka aircraft. The tests were not very successful, as was the case with the British and US tests of similar aircraft launching and recovery techniques. However, they did demonstrate that if an aircraft could be launched and recovered, it would provide a very valuable extension to the submarine's 'field of view', allowing it to survey hundreds of square miles rather than only the sea around it. Since Japanese naval strategy envisioned using submarines to locate an enemy battle fleet, so that its own battle fleet could come up and destroy it, this was obviously a highly desirable attribute. Further experiments were authorized.

The next step forward came with the conversion of the I-51, a Kaidai I class submarine based on German World War I designs, built in 1924. In 1930 a hangar large enough to accommodate two aircraft was installed abaft her conning tower, along with a compressed-air-powered catapult along her after deck. The Japanese copied the British Parnall Peto submarine-launched biplane, as carried by HM Submarine M2 (mentioned above), producing the Yokosuka E6Y1, also known as the Naval Type 91 light reconnaissance seaplane. It used the same Armstrong Siddeley Mongoose engine as the Peto.

Yokosuka E6Y1

Tests of the E6Y1 continued aboard the I-51 for three years, demonstrating that the submarine could launch and recover its aircraft in calm to moderate sea conditions. After three years, the hangar and catapult were removed from I-51, which reverted to normal submarine operations.

Japan was ready to move from experimentation to operational deployment of submarine aircraft carriers. She would go on to build no less than 42 such ships before and during World War II. Indeed, one of the paradoxes of the war was that Japan built larger, more powerful submarines than any other nation, but did so using poor workmanship, and handicapped them operationally with extremely unwise tactics. The latter never developed much beyond employing submarines as scouts for the fleet, or - later in the war - as resupply vessels for garrisons cut off by the US advance across the Pacific, and evacuation craft for senior officers and VIP's threatened by US forces. As a result, their crews paid a terrible price.

As one source points out:

Because of the vastness of the Pacific, Japan built many boats of extreme range and size, many of which were capable of cruises exceeding 20,000 miles and lasting more than 100 days. In fact, Japan built what were by far the largest submarines in the world, indeed, the only submarines over 5,000 tons submerged displacement, or submarines over 400 feet in length until the advent of nuclear power. These same boats were credited with a range of 37,500 miles at 14 knots, a figure never matched by any other diesel-electric submarine. These large boats could each carry three floatplane bombers, the only submarines in history so capable. Japan built 41 submarines that could carry one or more aircraft, while the vast submarine fleets of the United States, Britain, and Germany included not one submarine so capable.

During the Second World War, there were 56 submarines larger than 3,000 tons in the entire world, and 52 of these were Japanese. Japan built 65 submarines with ranges exceeding 20,000 miles at ten knots, while the Allies had no submarine capable of this feat. By 1945, Japan had built all 39 of the world's diesel-electric submarines with more than 10,000 horsepower, and all 57 of the world's diesel-electric submarines capable of 23+ knots surface speed.

The Japanese navy also built submarines with the fastest underwater speeds of any nation's combat submarines. They employed 78 midget submarines capable of 18.5 to 19 knots submerged, and built 110 others capable of 16 knots. As the war was ending they completed four medium-sized submarines capable of 19 knots submerged. This exceeds the 17.5-knot performance of the famed German Type XXI coming into service at the same time. As early as 1938, Japan completed the experimental Submarine Number 71, capable of more than 21 knots submerged.

Submarine Number 71 in 1938

Japanese submarines employed the best torpedoes available during the Second World War. The Type 95 torpedo used pure oxygen to burn kerosene, instead of the compressed air and alcohol used in other nation's torpedoes. This gave them about three times the range of their Allied counterparts, and also reduced their wake, making them harder to notice and avoid. The Type 95 also had by far the largest warhead of any submarine torpedo, initially 893 pounds (405 kg), increased to 1210 pounds (550 kg) late in the war. All Japanese torpedoes made during the war used Japanese Type 97 explosive, a mixture of 60% TNT and 40% hexanitrodiphenylamine. Most importantly, the Type 95 used a simple contact exploder, and was therefore far more reliable than its American counterpart, the Mark 14, until the latter was improved in late 1943.

Type 95 torpedo

Japan also developed and used an electric torpedo, the Type 92. This weapon had modest performance compared to the Type 95, but emitted no exhaust and, therefore, left no wake to reveal its presence. Similar electric torpedoes were used by several nations.

Given their size, range, speed, and torpedoes, Japanese submarines achieved surprisingly little. This was because they were mainly employed against warships, which were fast, maneuverable, and well-defended when compared to merchant ships. Japanese naval doctrine was built around the concept of fighting a single decisive battle, as they had done at Tsushima 40 years earlier. They thought of their submarines as scouts, whose main role was to locate, shadow, and attack Allied naval task forces. This approach gave a significant return in 1942 when they sank two fleet carriers, one cruiser, and a few destroyers and other warships, and also damaged two battleships, one fleet carrier (twice), and a cruiser. However, as Allied intelligence, technologies, methods, and numbers improved, the Japanese submarines were never again able to achieve this frequency of success.

. . .

For their disappointing achievements, Japanese submarines paid heavily. Japan started the war with 63 ocean-going submarines (i.e., not including midgets), and completed 111 during the war, for a total of 174. However, three-quarters of these (128 boats) were lost during the conflict, a proportion of loss similar that experienced by Germany's U-Boats. Most of the surviving boats were either dedicated to training roles or were recently completed and never saw combat. Of those which saw significant combat, the toll was very grim indeed. For example, of the 30 submarines that supported the Pearl Harbor attack, none survived the war.

Compared to German submarines, Japan's huge boats were relatively easy to sight visually and with radar, slow to dive, hard to maneuver underwater, easy to track on sonar, and easy to hit. Japanese hulls were also not as strong as those of German boats, and therefore could not dive as deeply nor survive such rough treatment. Also, they lacked radar until the first sets were installed in June 1944, and never had sets as good as the Allies possessed.

Compounding these deficiencies, Japan was at war with the United States and the United Kingdom, two nations embroiled in a vast conflict with hundreds of U-Boats in the Atlantic, and hence two nations which poured lavish resources into anti-submarine warfare (ASW) research and development. As an example of the fruits of this research, in June 1944 the US Navy sank the I-52 by using code-breaking to discover her schedule, finding her at night with radar-equipped carrier-based aircraft, tracking her underwater with sonobuoys dropped by those aircraft, and sinking her with acoustic homing torpedoes dropped by the same aircraft.

Japanese cargo submarine I-52, sunk by US naval forces
in the Atlantic Ocean in 1944
, while on a secret mission to Germany

The Japanese could achieve none of these technological feats at that time.

The only enemy aircraft to bomb the continental United States during World War II was a submarine-launched Yokosuka E14Y, known to US forces under the reporting name 'Glen'.

Yokosuka E14Y

It was launched from submarine I-25 on September 9th, 1942, off the coast of Oregon near Brookings, and flew two missions to drop small incendiary bombs, intended to cause forest fires. However, damp conditions prevented a conflagration. A more detailed account of the raid may be found here.

The biggest submarines of World War II were Japanese: the two Type AM vessels of 4,762 tons submerged displacement (I-13 and I-14) and three I-400 class ships of 6,560 tons (I-400, I-401 and I-402).

Model of I-400 class submarine (click the image for a larger view)

All were completed towards the end of the war, but only I-13 saw action - which was unfortunate for her crew, as she was sunk by US forces in July 1945. The AM ships could carry two Aichi M6A Seiran floatplane dive/torpedo bombers in watertight hangars, and the I-400's three.

Aichi M6A Seiran

The M6A was intended to attack targets such as the Panama Canal and Ulithi Atoll, a major US naval base (details of the proposed operations are at the links). However, rumors of a planned bacteriological warfare attack against the US mainland have not (as far as I'm aware) been confirmed from reliable Japanese sources. They appear to be the product of over-fertile Hollywood-influenced imaginations.

At the end of the war, the United States took possession of all surviving Japanese submarines. The big aircraft-carrying subs surprised their American captors, who'd never before seen any submarine that large. The I-400 class, in particular, were almost three times the displacement of a US Gato class fleet submarine.

(L-R) I-14, I-401 and I-400 in Tokyo Bay, September 1945.
Their Japanese crews are still aboard, awaiting interrogation.
(Original image owned by R. Hedman of Click it for a larger view.)

In an effort to keep such technology out of the hands of the Soviet Union and other powers, the US sank most of the advanced Japanese submarines, and repatriated several others - including two I-400's and two high-speed I-201 class vessels - to Hawaii.

I-400 in dry-dock at Pearl Harbor, Hawaii, in 1946.
Note the open hangar door below her conning tower.

There they were tested and evaluated before being sunk off Oahu in 1946.

A US Navy sailor examines the hangar door of an I-400 class submarine

One of them, I-401, made headlines when it was rediscovered on the ocean floor by a University of Hawaii underwater expedition in 2005.

Conning tower of I-401, photographed off Hawaii in 2005

Here's video footage of the discovery of the remains of the sunken Japanese subs, followed (at the 2 min. 14 sec. mark) by film taken in 1945 of the submarines when first captured, showing details of the I-400 class aircraft hangar, and the repatriation of the subs to Hawaii.

The Germans also tried to use aircraft - or, rather, aircraft-like devices - from submarines during World War II, to increase the visual search radius. They attempted to develop a collapsible floatplane, the Arado Ar 231, which would fit into watertight canisters secured to the U-boat's hull.

Arado Ar 231 being lowered into the sea by the German raider Stier

Six prototypes were built, but the Ar 231 was found to be far too delicate and damage-prone to handle the rough-and-tumble of shipboard life. Two were shipped aboard the commerce raider Stier, but her captain later indicated that he regretted doing so. They were never used aboard a submarine.

As an alternative, the Kriegsmarine turned to the Focke-Achgelis FA 330 Bachstelze, or 'Wagtail'.

FA 330 at the National Museum of the USAF, Dayton, Ohio

This was an unpowered glider utilizing the autogyro principle: a rotating series of blades provided lift, but were spun by air speed, provided by a towing vehicle - in this case, a U-boat. (After World War II, British evaluators towed them behind Jeeps and other light vehicles, with good results.)

FA 330 being deployed atop the conning tower of a U-boat during World War II

The FA 330 would be towed at an altitude of 300-400 feet, extending an observer's radius of vision to 25 miles instead of the approximately 5 miles available from the submarine's conning tower. However, it took about 20 minutes to assemble or disassemble, far too long for use in areas where enemy anti-submarine aircraft might appear at any moment. For that reason, it was used more in distant operational areas, such as the South Atlantic and Indian Oceans, where the risk of enemy observation was much lower. This led to the device being uncovered when U-852 was bombed by aircraft from 8 Squadron on May 2nd, 1944, and driven ashore on Cape Guardafui in what is today Somalia.

Wreck of U-852 after beaching on Cape Guardafui

British forces found an intact FA 330 aboard the wreck, which aroused great interest. U-852's captain and two other crew members would later be executed for war crimes.

Germany also developed the Flettner FL 282 Kolibri, or 'Hummingbird', an intermeshing-rotor helicopter.

It underwent extensive testing, including shipboard trials in 1941 aboard the cruiser Köln. It was considered useful as a maritime observation platform, and in 1944 the aircraft was ordered into production. However, the BMW factory at Munich, where it was scheduled to be produced, was destroyed by Allied bombs, and the aircraft never went into operational service with the Kriegsmarine (although it saw limited use as an Army observation aircraft). Nevertheless, it's considered one of the first successful helicopters.

Germany also wanted to fire the Fieseler Fi 103 (better known as the V-1 'buzz bomb') from submarines. Nothing came of this during World War II, but after the war, the USA experimented with firing its version of the Fi 103 (known as the JB-2 Loon) from the decks of two submarines, the USS Carbonero and USS Cusk.

USS Cusk firing JB-2 Loon missile (click the image for a larger view)

Both submarines (and others following them) were subsequently refitted to launch the SSM-N-8 Regulus cruise missile.

USS Tunny launching SSM-N-8 Regulus missile

The Soviet Union also deployed cruise missiles aboard its submarines, for example, the P-5 Pyatyorka, shown below in its twin cylinders aboard a Whiskey class vessel.

However, by the 1960's, these early nuclear-tipped cruise missiles were rendered obsolete by more modern ballistic missiles. The age of submarine-launched aircraft appeared to be over.


For several decades submarines have made steady progress as undersea fighting vehicles. Nuclear-powered vessels are used exclusively by the US Navy and the British Royal Navy, and to a large extent by Russia. France and China have some nuclear-powered and some conventional submarines, while India is leasing a nuclear boat from Russia and has ambitions to build its own in due course.

However, none of these vessels has been designed to fight on the surface, as the old big-gun submarines would do, or launch aircraft to strike at a distance or carry out reconnaissance. Their main weapon for anti-submarine warfare has remained the guided torpedo, with missiles added to their arsenal for anti-surface-vessel strikes. Some carry modern cruise missiles for strikes against terrestrial targets. (This excludes ballistic missile submarines, of course, whose main weapons are designed to destroy entire cities and nations rather than point targets or ships.)

This may be about to change.

The French naval company DCNS has put forward a conceptual study that abandons much of what's assumed to be conventional wisdom about modern submarines, and in many ways reverts to the 'cruiser submarine' concept. They call it the SMX-25.

(Click the images for a larger view)

According to Bill Sweetman, writing in Ares (who says it looks like a 'running shoe'!):

It doesn't look like other submarines because it's designed for a different job - primarily, anti-surface warfare, rather than anti-submarine warfare. That changes everything. The submarine needs mobility to catch and stay up with surface ships. It will be optimized for survival against active, not passive sonar. It needs a heavy missile load, ready to fire, because surface ships travel in groups and multiple shots can overwhelm the defenses.

Non-nuclear submarines can't run fast for long: batteries don't store enough energy, their circular-section hulls aren't efficient on the surface, and wave effects limit snorkeling speed to 11 knots or so. SMX-25 is therefore designed for high speed on the surface, with a wave-piercing hull and retractable air inlets for three 16 MW gas turbines driving waterjets. Top speed is 38 knots and range at 14-20 knots is 8000 nm.

In action, SMX-25 can ballast to a semi-submerged position with the sail above the surface. It can still run on turbines, the sail is a small visual or radar target, and all 16 missile tubes are ready to fire. Finally, the boat can submerge completely and run on diesel (via a snorkel) or batteries, driving retractable motor-propeller units.

It's a big submarine for a non-nuke, 360 feet long with a surface displacement of 2850 tonnes and 5460 tonnes submerged. under the water, the hull is faceted rather than rounded - like a stealthy aircraft, faceting weakens back-scattered echo from an active sonar.

DCNS argues that the SMX-25 could be remarkably survivable. It is a small target for surface attack - and if engaged by a missile it can dive. Its speed makes it a tough target for a torpedo, and it has sensors above and below the water. And although it looks like something out of Thunderbirds, it is designed entirely around existing technology.

I find this intriguing in the light of historical developments. The SMX-25 is a lot slower underwater (10 knots) than most modern submarines; but that's not where it's going to spend most of its time. It's a return to a 'submersible' rather than a true submarine, just as, prior to the advent of air-independent propulsion systems (of which nuclear power is the best known), all submarines were effectively 'submersible surface ships', not capable of staying at depth for very long.

Furthermore, DCNS states that the ship "will be equipped to deploy combat swimmers and their delivery vehicles, commandos, unmanned underwater vehicles (UUVs) and unmanned aerial vehicles (UAVs)". That's where it's at, today. Think of something like this as an ultra-high-speed, dash-in-and-get-out SEAL delivery system. Its stealth characteristics will make it very hard for an enemy to detect . . . until the explosions start, of course!

If the SMX-25 can deploy small UAV's, or even larger ones such as the Northrop Grumman MQ-8 Fire Scout, shown below;

or Boeing A160 Hummingbird;

it becomes a real game-changer. Such UAV's can be equipped with light torpedoes or short-range missiles, to supplement the heavier weapons carried by the SMX-25 'mother ship', thus providing a great deal of flexibility for littoral operations. The submarine itself would not have to carry light weapons to deal with limited threats if it can hang such weapons off a UAV.

Similarly, minesweeping and mine hunting operations increasingly rely on UUV's to locate and neutralize naval mines. A submersible such as the SMX-25 could carry a number of such UUV's, and release them to operate in a circular pattern around it, not only clearing the way ahead of it, but preventing other threats - for example, torpedoes, or other submarines, or surface vessels - from getting too close without being detected. In effect, it could operate as the 'queen bee' for a 'hive' of UAV's and UUV's, sanitizing and controlling an area of hundreds, even thousands of square miles above, on and below the surface of the sea.

For land attack missions, instead of bombarding enemy positions with large cannon, the SMX-25 could use UAV's to conduct distant reconnaissance without ever exposing itself to counter-fire. It could then launch its large missiles, or send in UAV's with smaller weapons (or special forces troops carried aboard it) to destroy targets with pinpoint accuracy. It might even quickly assemble and launch fixed-wing UAV's similar to the Predator or Reaper, or a faster, more powerful replacement such as the Avenger, using a deck-mounted catapult or rail, to carry bombs or missiles to the target. Shades of the old M2, I-400 and Regulus subs! Its size is also reminiscent of its predecessors - its submerged displacement is about halfway between the Japanese Type AM and I-400 class boats.

The only area where I can see possible shortcomings is in underwater combat with other submarines, which will be faster and (probably) quieter in that environment. However, given the assistance of a 'globe' of UUV's around it, the SMX-25 might be able to give a very good account of itself; and, if necessary, it can surface and use its very high speed to 'get out of Dodge', leaving slower conventional submarines floundering in its wake. Of course, a nuclear boat will be able to keep up with it, but it'll make a small, difficult target at such speeds. Indeed, some torpedoes won't be able to home on it at all, because they'll have to move so fast to catch it that the noise generated by the high-speed rush of water past their sensors will 'blot out' the sound signature of their target.

For nations wanting to guard a maritime choke-point such as the Malacca Strait, or the Strait of Hormuz, or the Strait of Gibraltar, something like the SMX-25 might be an extremely useful defensive tool. For nations wanting to force their way through such choke-points, the SMX-25 might be a nightmare! Just how do you counter it? Fire missiles at it? It can submerge, out of their reach, and resurface as soon as they've run out of fuel and crashed. Fire torpedoes at it? You've got to get close enough to do that without being detected - not easy in a littoral situation - and it can outrun many torpedoes and use countermeasures against the rest, even while it fires missiles and torpedoes back at you. Bomb it from the air? It has anti-aircraft missiles it can use against you . . . and if it's near friendly territory, it'll probably have an air escort of its own.

Of course, the SMX-25 is purely a concept at present. No-one's placed an order for it, and it may never go into production. Nevertheless, it's an interesting example of 'thinking outside the box' in naval architecture; and with today's renewed emphasis on littoral combat (the US Navy is building an entire class of ships to deal with that environment), the SMX-25 may become more than just a distant gleam in someone's eye. If it can be built economically, who knows? The long-dead crews of the big-gun and aircraft-carrying submarines of yore may get to sit up and take notice in Davy Jones' locker, as one of these beasts cruises overhead!

I'll be watching this concept with considerable interest.



trailbee said...

The evolution of designs and technologies is incredible, bringing global size to its knees. Who will be first to build one of these prototypes, and for what purpose. It's a whole new ball game, and so interesting. Thank you.

Roy said...

If you are interested in the history of submarines, you might be interested in the following site - "Through the Looking Glass"

Home on the Range said...

Excdellent. My big brother works at Electric Boat Division of General Dynamics. I grew up with the stories of the subs (he was on the one that was part of Operation Ivy Bells). GREAT article and photos.

trailbee said...

If that was for me, I went there and loved this site. Thanks.

Anonymous said...

I admit I'd get a charge out of seeing a submarine firing a large-bore naval rifle from periscope depth!

Thank you Peter, for all the time and effort you put into this. I enjoyed reading it a lot.


Ol' Lurker said...

Fascinating stuff that I don't find elsewhere. Many thanks for your hard work. It's this kind of stuff that makes many of us keep coming back.

Aggie said...

Oy Vey!

Thanks, Peter.

God Bless Ya'll!

Aggie, Class of '70
An Anglican Firearms "Enthusiast" (ie: Gun Nut)

Anonymous said...

Thank you!
Very interesting overview.
Sometimes I wish that my Navy nuke kid had gone subs, rather than carriers.

-- ARRognlie

Unknown said...

Probably one of the more informative articles I've had the pleasure of reading in a while. Thank you for giving a good overview of a little known section of submarine warfare.