HYBRID

AIRCRAFT

CARRIERS

More Fanciful Than Practical…

…But a Concept That Still Intrigues

~ BACKGROUND ~

In the early 19th and 20th centuries, battleships, which were often referred to as capital or ‘big gun’ ships, were a symbol of naval dominance and a source of national pride. For several decades they played an important role in the projection of sea power. No self-respecting world power’s navy was considered complete without having at least one battleship.

Then along came naval aviation and eventually the cataclysmic events in naval history that transpired in 1941/942. Such as the sneak attack on Pearl Harbor, the sinking of two British capital ships a few days afterwards and the Battle of Midway; amongst other events in which air power reigned supreme. At first relegated to a support role…scouting for battle fleets…eventually the aircraft carrier replaced the battleship as the symbolic capital ship in numerous navies.

But during a lengthy and often contested transition period, ‘battleship admirals’ resisted that shift and only grudgingly agreed to experiment with a curious combination of ship types that were dubbed hybrids. Several nations participated in what ultimately proved to be an ill-advised and largely unworkable way to wage war by incorporating aircraft carrying capabilities into the designs of traditional ‘big gun’ ships…and also submersibles.

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~ EARLY EXPERIMENTS ~

In the early 20th century, several world powers demonstrated that aircraft could take off and land at sea, using improvised platforms temporarily mounted on existing warships. One of the first, if not the first, was the United States Navy. The birth of naval aviation in America took place on November 14, 1910, when a civilian aviator flew his flimsy airframe from an anchored cruiser’s improvised flight deck. This noteworthy event was followed two months later when that same daring pilot landed on another anchored US Navy warship, temporarily modified for the purpose of demonstrating the feasibility of shipboard aircraft operations. Aircraft operations conducted from ships while underway commenced in 1912, when an aircraft flew off a temporary platform mounted on the bow of a British cruiser. The world’s first air raid conducted by naval forces was made in 1914 by four amphibian aircraft supported by a Japanese seaplane tender. Interestingly, Japan was a member of the allies in World War I, and that historic attack was made against an Austro-Hungarian cruiser and a German gunboat. However, neither vessel was hit.

The first ‘true’ aircraft carrier was HMS ARGUS; commissioned in 1918. Originally slated to be an Italian ocean liner, World War I prevented her being completed in that configuration by her British shipbuilders. Instead, she became a Royal Navy flush-deck carrier. ARGUS was often derisively called a ‘covered wagon’ before she proved her worth in World War II.

But such ships, capable of launching and recovering aircraft at sea were at first only considered as support ships for fleets of ‘big gun’ warships. Then, someone in the Royal Navy came up with the idea of combining the capabilities of ‘battlewagons’ with ‘covered wagons’.

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~ HMS FURIOUS…FIRST OF THE HYBRIDS ~ HMS FURIOUS and two ‘half-sister’ ships, as designed, were intended to be lightly protected, high speed battlecruisers. With a length of 786.75 feet and a beam of 88 feet, they were expected to displace a calculated 22,890 tons at full load. They were the first large British warships to have geared turbines, and were expected to attain a maximum speed of 31.5 knots. HMS GLORIOUS and COURAGEOUS (below), as completed, were fitted with a main armament of four, 15-inch naval rifles. FURIOUS, however, initially had installed two massive 18.1-inch guns mounted in two single turrets; one forward and one aft; hence the three ships’ designation as ‘half-sisters’.

Shortly after completion, FURIOUS returned to her builder’s yard, when her forward gun turret was removed and replaced with an aircraft hanger and a 228 foot long flight deck that was 50 feet wide. The hangar was capable of storing ten aircraft. A crane was utilized to lift aircraft from the hangar to the flight deck. The ship was assigned several floatplanes, which utilized a wheeled trolly that ran on a track down the centerline of the vessel’s flight deck for take-off.

Commissioned in June of 1917, FURIOUS…first of the hybrid aircraft carriers…initially used the crane to recover aircraft after they landed alongside her. But that practice proved to be unworkable in rough seas. On August 2, 1917, a never-before attempted maneuver was tried. The idea was to land on the vessel’s flight deck by flying alongside the ship and side-slipping around the ship’s superstructure and onto the flight deck. A Sopwith Camel fitted with conventional landing gear and being flown by Squadron Commander E. H. Dunning approached the ship, moving slowly forward along its starboard side. FURIOUS was steaming at 26 knots with a 21-knot headwind over its flight deck.

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As a result, Commander Dunning’s aircraft could essentially hover alongside FURIOUS. When he adroitly maneuvered sideways and over the flight deck, members of the ship’s crew, served as an impromptu human arresting gear system; risking life and limb to grab the aircraft’s structure and help settle it into what was the world’s first ever landing on a moving ship. Tragically, five days later, when attempting to repeat his feat, the engine on Commander Dunning’s airplane stalled. He crashed into the sea and drowned. Soon thereafter the FURIOUS received another major modification. Near the end of 1917, her aft gun turret was removed and replaced by a 300 foot long landing deck; surmounted by a second hangar. Two aircraft elevators, called ‘lifts’ by the British, were installed, one for each hanger. Her superstructure and funnel were left intact, but were flanked on either side by narrow aircraft taxi strips that connected the landing deck, aft and the take-off deck, forward.

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However, turbulance generated by the ship’s superstructure and single centerline funnel while underway at high speed made landing on FURIOUS’ aft flight deck hazardous. Another disarming factor was the relative shortness of the landing area. A contraption that consisted of suspended vertical wires had to be installed to prevent any aircraft missing the ship’s primative arresting gear from crashing into the large funnel. Nevertheless, Britian’s hybrid aircraft carrier and her embarked squadrons made history on July 19, 1918, when they made the world’s first carrier-based air strike. Their mission, to bomb a German Zeppelin base was a success; albeit only resulting in minor damage to the German installation. A few months later, at the end of World War I, FURIOUS was laid up. Economic considerations precluded the construction of a full-fledged carrier. Rather than scrapping her, the Royal Navy modifed not only her, but also converted her two half-sisters from their original configurations as battle cruisers to become true aircraft carriers, as depicted below.

FURIOUS survived World War II, only to be scrapped in 1948. COURAGEOUS and GLORIOUS were both sunk during the early years of the war; in 1939 and 1940, respectively.

~ FLYING-DECK CRUISERS ~

The Washington Naval Treaty, which was a multi-nation agreement created after World War I to limit the size of the world’s navies, had a great deal to do with the US Navy toying with the concept of ‘Flying-Deck Cruiser’. So did the reluctance of America’s battleship admirals to accept aircraft carriers that could not defend themselves if engaged in combat with powerful enemy surface ships. Thus was conceived the idea of a hybrid vessel of approximately 10,000 tons displacement (to meet treaty limitations) that had the attributes of a cruiser and a carrier. Such a vessel would have been about 650 feet long. The forward half of the vessel was to be fitted with one or more large caliper gun turrets. The after half was to have a 350 foot long flight deck atop a hangar capable of handling twenty-four aircraft, plus a starboard side island that included uptakes from the ship’s boilers; see the c.1930s design drawing, top of the next page.

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No flying-deck cruisers were ever built by the United States. Instead, two battle cruisers under construction were modified extensively to create the large carriers LEXINGTON (CV-2) and SARATOGA (CV-3). Although they were ‘pure’ aircraft carriers, the Navy brass was not convinced that their aircraft, alone could adequately protect them from a surface attack. So, initially they were fitted with four large gun turrets, resulting in a so-called ‘half-hybrid’ design. These turrets were each fitted with two, eight-inch naval rifles and placed along the starboard side of the ships’ flight decks; two forward and two aft of massive island structures. The eight-inch guns were intended to provide as a means of repelling surface ship attacks. They could not be sufficiently elevated to ward off dive bombers, plus their large caliber design would have made them ineffective against such targets. In addition, the positioning of the original gun turrets made firing to the port side difficult, especially when aiming at surface targets at close range. Plus, the muzzle blast from any such attempt would have easily damaged embarked aircraft and the flight decks’ wooden sheathing. During World War II, both carriers had these large-bore gun turrets replaced by dual-purpose, five inch weapons more suitable for antiaircraft purposes.

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~ STILL-BORN BATTLESHIP/CARRIER HYBRIDS ~

At least two other nations considered the idea of building or modifying battleships that incorporated aircraft carrier capabilities.

The French gave some thought to modifying their biggest battleship, the JEAN BART, and created this imaginative isometric illustration. But that is all they ever produced in the way of a hybrid battleship/carrier. During the 1930’s, the Russian government commissioned the American naval architecture design firm of Gibbs & Cox to utilize the following design parameters to develop a formidable battleship/aircraft carrier concept.

Length: 1,005 feet; Beam: 128 feet; Displacement, F ull Load: 74,000 tons

Main Armament: 12 – 16 inch guns; Aircraft: 36; Elevator s: 2

Armor Belt, Hull: 13 inches; Turret Faces: 16 inche s; Boilers: 13; Shafts: 6

Total Shaft Horsepower: 300,000; Max. Speed 34 knots; Com plement 2,706

This idea never was developed any further; no doubt due to the advent of World War II. But during that conflict, two existing battleships did become hybrid CVs.

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JAPAN’S WORLD WAR II HYBRIDS ~ Japan was firmly committed to the use of aircraft carriers at the start of World War II. But the loss of several of their frontline carriers at the Battle of Midway, plus later losses prompted them to consider converting two of their battleships to large flush deck carriers, capable of carrying 54 aircraft each. This plan was abandoned due to the lack of resources and the long period of time that such radical modifications would have required. Instead the battleships ISE and HYUGA, built in the early 20th century and considered obsolete when World War II began were selected to become hybrid battleships/carriers. The two aftermost main gun turrets and associated heavily armored barbettes of each of these older battleships were removed and replaced by a hangar, a 230 foot long flight deck and a single T-shaped elevator. Each ship was capable of carrying 22 aircraft. Several fourteen-inch guns and towering ‘pagoda’ bridge and fire control structures were retained in each ship. Other aircraft-related features included two catapults forward of the flight deck and a crane well aft on the port side. The removal of two gun turrets and barbettes resulted in a decrease of 1,700 tons per ship, resulting in an adverse effect on the ships’ stability. To partly compensate, each vessel’s flight deck was covered with eight inches of concrete due to the scarcity of armor plate. The conversion of these two vessels was completed in October of 1943, but it was a year later before trained pilots and enough aircraft could be provided for them to sortie with other units of the Japanese battle fleet, which by then was being rapidly depleted by Allied air, surface and submarine attacks. Neither ISE nor HYUGA distinguished themselves in battle. Their contributions were minor, at best. When the lack of fuel oil and replacement aircraft became acute, they both were laid up in early 1945. American aircraft attacked them repeatedly, resulting in ISE being sunk in Japanese shallow coastal waters and HYGUA being run aground to avoid sinking. They were both scrapped in 1947.

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~ RUSSIAN REDUX ~

Years later, during the height of the Cold War, Russian naval architects revived the concept of the hybrid aircraft carrier when the cost and complexity of creating vessels comparable to America’s supercarriers proved to be beyond their means. Instead, a smaller, but more contemporary than the 1937 design was selected.

Referred to as ‘aviation cruisers’, four units of what was called the KIEV-class were commissioned between 1975 and 1987. These ships were 896 feet long, with an extreme beam of 174 and displaced 45,000 tons. Each was fitted with a conventional steam propulsion plant that generated 200,000 shaft horsepower and allowed these vessels to attain a maximum speed of 32 knots. They had very large starboard side islands and an angled flight deck that ran roughly two-thirds of their length. The forward third of these ships was devoted to the installation of multiple missile launchers, giving them this fierce look. But their aircraft capacity was only twelve fighters and sixteen to twenty helicopters. From an operational standpoint, these hybrid vessels were a disappointment. When the Soviet Union imploded in 1991, all of them were laid up. Subsequently, three were sold; two to China and one to India. The fourth unit was scrapped.

The aviation cruiser sold to India underwent a conversion in Russia akin to the one in which HMS FURIOUS was converted from a hybrid to a conventional carrier at the end of World War I. However, when the flight deck was extended, it included a ‘jump-jet’ ski ram. This feature is shown on the left when the ship left Russia in July 2013.

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~ SUBMERSIBLE, SEMI-HYBRID CARRIERS ~ Submarines of several nations constituted the largest number of what are often called hybrid aircraft carriers. But when applied to submarines, that term is a bit of a misnomer. Semi-hybrid would perhaps be a more accurate, albeit obscure term. No submarine ever built could launch and recover aircraft from its deck.

The idea of launching aircraft from submarines originated in Germany in 1915. Experiments using U-12 and an amphibian reconnaissance aircraft, depicted on the left, were conducted, but with little success. Once outside protected waters, the aircraft was easily damaged and U-12 could not submerge quickly.

The Royal Navy conducted similar experiments towards the end of World War I; with equally disappointing results. In the late 1920s, the British converted one of their larger submarines, HMS M2. A hydraulic catapult was installed on its foredeck. In addition, a waterproof hangar was added just forward of the sub’s conning tower, which was topped with a derrick device for recovering aircraft. This allowed the submarine and her single seaplane to scout ahead of the battle fleet, and submerge when under threat of attack. In order to fit into the hangar, the aircraft’s wings were modified to fold back completely. M2 was lost in a 1932 accident that was later determined to be due to a failure of the watertight seal on the hangar’s hatch. By then, the Royal Navy had decided that subs capable of launching and recovering aircraft were not a good substitute for surface ships. Other navies also experimented with aircraft carrying submersibles between the two world wars, including the US Navy. Between 1922 and 1931, several schemes were proposed; none of which excited the battleship admirals any more than did conventional aircraft carriers.

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One idea advanced was to carry disassemblable seaplanes in small watertight compartments bolted to the deck of a submarine. Several such configured aircraft were actually purchased by the US Navy for evaluation and testing. Two such models of aircraft were tested at sea, using the American submarine S-1. But they were never deployed on any actual missions. In 1931, a design for a large amphibian, dubbed the Loening XSL-1, was tested in the large-scale wind tunnel at Langley Field, Virginia. Once again, senior naval officers in the United States vetoed fleet use of aircraft-carrying submarines. And that was the end of such experiments in the US Navy. However, two other nations, France and Japan did develop such weapons’ systems. In 1927, the French Navy ordered a large and unique submarine. Commissioned in 1934, the submerged displacement of SURCOUF was 4,000 tons; the largest submarine in any navy before the advent of World War II. Called an ‘underwater cruiser’, she carried an observation plane in a hangar aft of the conning tower and a twin, eight-inch gun turret forward.

But it was the Japanese Navy which advanced the concept and produced more aircraft-carrying submarines than all the other nations’ navies, collectively. In total, the Japanese built 47 submarines with the capability to carry seaplanes. Most of the Imperial Japanese Navy’s submarine aircraft carriers could only handle a single airplane. A few others could carry two, and the giant I-400 Class submarines, developed and deployed during World War II had the capability to carry as many as three aircraft in very large, waterproof hangars. The photo on the right shows American naval personnel inspecting one of those hangars at the end of the war.

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The most numerous of Japan’s aircraft carrying subs was called the B1 Type. Twenty of them were built and used during World War II with mixed results. These submersibles had more luck in the conventional manner; firing torpedoes at enemy targets. The B1 Type carried a single seaplane in hangars located forward of the subs’ conning towers. They were launched by catapult. One of them, I-25, made history in 1942 when its embarked airplane conducted the only aerial bombing on the continential United States in September 1942. Two small incendiary bombs were dropped on a forest near Brookings, Oregon. No real damage was done. A larger type of submarine, called AM, could carry two aircraft. But the biggest of then all were a trio of I-400 Class submarines. They were over 400 feet long and displaced 6,500 tons. Their size was not exceeded until the US Navy started building nuclear-powered, ballistic missile-firing submarines in the late 1950s. The huge hangars of the I-400 Class extended aft were partly located below their conning towers. They were also fitted with a large caliber deck gun, aft and a crane for recovering aircraft, and a catapult for launching aircraft forward.

None of the three accomplished anything memorable during World War II. Just before the formal end of the war, the crews of the two of them at sea were ordered to destroy their weapons. Torpedoes were fired without being armed, and the trio’s aircraft were catapulted into the ocean; wings still folded.

After inspecting all three of the I-400 Class thoroughly in Japan, the US Navy moved two of them to Hawaii utilizing prize crews composed of veteran American submariners. Those voyages were made entirely on the surface, which was difficult enough. The crews had no operating manuals they could read. Like the manuals, all equipment label plates were in Japanese. After further inspections in Hawaii, the two subs were used for target practice and sunk in very deep water in 1946. The remaining I-400 Class boat was likewise used as a target and sunk in the Western Pacific. Thus ended the era of the hybrid aircraft carrier. Or did it?

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~ FUTURE POTENTIAL FOR HYBRIDS ~ The closest thing to historic hybrid aircraft carriers that now exists is the helicopter-carrying amphibious assault ship. Although none of them boast any large caliber weaponry, they are fitted with a variety of missile launchers. Moreover, their versatility far exceeds the capabilities of hybrids of the early 20th century, since they can launch and recover amphibious landing craft as well as helicopters and vertical take-off and landing (STOVL) aircraft. The introduction of unmanned aircraft (drones) into the US Navy’s inventory also may lead to the return of the concept of submersible hybrid aircraft carriers. But in an expanded sense, resulting in a true hybrid, capable of supporting the launch and recovery of contemporary ‘aircraft’ far beyond the imagination of even the most ambitious of hybrid supporters in the early 20th century. It does not take much in the way of creative thought to envision a submarine fitted with a hangar and a catapult; suitable for launching and recovering drones while the vessel is surfaced. But to take that one step further, why not create a drone launching and recovery system for a submerged mother ship? Underwater launching should be relatively easy, perhaps patterned after proven ballistic and tactical missile launch systems already in use. Recovery would be a little harder. Well, maybe a lot harder. But not technically impossible. Skeptics once said that launching of ballistic missiles from submerged vessels was only a dream, and was ‘never gonna happen’. They were quickly proven wrong. It has been well publicized that the US Navy is currently working on what is called a universal drone launch and recovery system that will be readily adaptable to current design submarines for underwater use. You can bet other nations’ navies are doing the same thing. It’s just a matter of time…

Bill Lee May 2017