The Graf Zeppelin-class aircraft carriers''' were four German Kriegsmarine aircraft carriers that were planned in the mid-1930s by Grand Admiral Erich Raeder as part of the Plan Z rearmament program after Germany and the United Kingdom signed the Anglo-German Naval Agreement. They were planned after a thorough study of Japanese carrier designs. German naval architects ran into difficulties due to lack of experience in building such vessels, the realities of carrier operations in the North Sea and the lack of overall clarity in the ships' mission objectives.
This lack of clarity led to features such as cruiser-type guns for commerce raiding and defense against British cruisers, that were either eliminated from or not included in American and Japanese carrier designs. American and Japanese carriers, designed along the lines of task-force defense, used supporting cruisers for surface firepower, which allowed flight operations to continue without disruption and reduced the chances of exposure to risks that surface action would have entailed.
A combination of political infighting between the Kriegsmarine and the Luftwaffe, disputes within the ranks of the Kriegsmarine itself and Adolf Hitler's waning interest all conspired against the carriers. A shortage of workers and materials slowed construction still further and, in 1939, Raeder reduced the number of ships from four to two. Even so, the Luftwaffe trained its first unit of pilots for carrier service and readied it for flight operations. With the advent of World War II, priorities shifted to U-boat construction; one carrier, , was broken up on the slipway while work on the other, (christened Graf Zeppelin) was continued tentatively but suspended in 1940. The air unit scheduled for her was disbanded at that time.
The role of aircraft in the Battle of Taranto, the pursuit of the German battleship , the attack on Pearl Harbor and the Battle of Midway demonstrated conclusively the usefulness of aircraft carriers in modern naval warfare. With Hitler's authorization, work resumed on the remaining carrier. Progress was again delayed, this time by the demand for newer planes specifically designed for carrier use and the need for modernizing the ship in light of wartime developments. Hitler's disenchantment with the performance of the Kriegsmarine's surface units led to a final stoppage of work. The ship was captured by the Soviet Union at the end of the war and sunk as a target ship in 1947.
Design and construction
After 1933, the Kriegsmarine began to examine the possibility of building an aircraft carrier.Gardiner & Chesneau, p. 226 Wilhelm Hadeler had been Assistant to the Professor of Naval Construction at the Technische Hochschule in Charlottenburg (now Technische Universität Berlin) for nine years when he was appointed to draft preliminary designs for an aircraft carrier in April 1934.Reynolds, p. 42 Hadeler's first design was a ship that could carry 50 aircraft and steam at .
The Anglo-German Naval Agreement, signed on 18 June 1935, allowed Germany to construct aircraft carriers with total displacement up to 38,500 tons,Reynolds, p. 43 though Germany was limited to 35% of total British tonnage in any category of warship. The Kriegsmarine then decided to scale back Hadeler's design to , which would permit the construction of two ships within the 35% limit.
The design staff decided that the new carrier would need to be able to defend itself against surface combatants, which necessitated armor protection to the standard of a heavy cruiser. A battery of sixteen guns were deemed sufficient to defend the ship from destroyers.Gardiner & Chesneau, pp. 226–227 In 1935, Adolf Hitler announced that Germany would construct aircraft carriers to strengthen the Kriegsmarine. A Luftwaffe officer, a naval officer, and a constructor visited Japan in the autumn of 1935 to obtain flight deck equipment blueprints and inspect the Japanese aircraft carrier .Reynolds, p. 44 The Germans also unsuccessfully attempted to examine the British carrier .Gardiner & Chesneau, p. 227
The keel of Graf Zeppelin was laid down on 28 December 1936, on the slipway that had recently held the battleship . The ship was built by the Deutsche Werke shipyard in Kiel.Gröner, p. 71 Two years later, Großadmiral Erich Raeder presented an ambitious shipbuilding program called Plan Z which would build up the Kriegsmarine to a point where it could challenge the British Royal Navy in the North Sea. Under Plan Z, by 1945 as part of the balanced force the navy would have four carriers; the pair of Graf Zeppelin-class ships were the first two in the plan. Hitler approved the construction program on 1 March 1939.Gardiner & Chesneau, p. 220 In 1938, a second carrier, ordered under the provisional name "B", was laid down at the Germaniawerft dockyard in Kiel.Gröner, pp. 71–72 Graf Zeppelin was launched on 8 December 1938.Gröner, p. 72
Design
Hull
The Graf Zeppelin class's hull was divided into 19 watertight compartments, the standard division for all capital ships in the Kriegsmarine.Breyer, p. 33 Their belt armor was to vary from over the machinery spaces and aft magazines, to over the forward magazines and tapered down to at the bows. Stern armor was kept at to protect the steering gear. Inboard of the main armor belt was a anti-torpedo bulkhead.Whitley (1985), p. 157
Horizontal armor protection against aerial bombs and plunging shellfire started with the flight deck, which acted as the main strength deck. The armor was generally thick except for those areas around the elevator shafts and funnel uptakes where thickness increased to in order to give the elevators necessary structural strength and the critical uptakes greater splinter protection. Beneath the lower hangar was the main armored deck (or tween deck) where armor thickness varied from over the magazines to over the machinery spaces. Along the peripheries, it formed a 45 degree slope where it joined the lower portion of the waterline belt armor.
The Graf Zeppelins original length-to-beam ratio was 9.26:1, resulting in a slender silhouette. However, in May 1942, the accumulating top-weight of recent design changes required the addition of deep bulges to each side of Graf Zeppelins hull, decreasing that ratio to 8.33:1 and giving her the widest beam of any carrier designed prior to 1942.Brown, p. 9 The bulges served mainly to improve Graf Zeppelins stability but they also gave her an added degree of anti-torpedo protection and increased her operating range because selected compartments were designed to store approximately 1500 additional tons of fuel oil.Whitley (1984), p. 31Graf Zeppelins straight-stemmed prow was rebuilt in early 1940 with the addition of a more sharply angled "Atlantic prow", intended to improve overall seakeeping. This added to her overall length.Breyer, p. 33
Machinery The Graf Zeppelin class's power plant was to consist of 16 La Mont high-pressure boilers, similar to those used in the heavy cruisers. Their four sets of geared turbines, connected to four shafts, were expected to produce and propel the carrier at a top speed of . With a maximum bunkerage capacity of 5000 tons of fuel oil (prior to the addition of bulges in 1942), the Graf Zeppelins calculated radius of action was at . However, wartime experience on ships with similar power plants showed such estimates were highly inaccurate, and actual operational ranges tended to be much lower.Whitley (1985), p. 159
Two Voith-Schneider cycloidal propeller-rudders were to be installed in the forward bow of the ship along the center-line. These were intended to assist in berthing the ship in harbor and also in negotiating narrow waterways such as the Kiel Canal where, due to the carrier's high freeboard and difficulty in maneuvering at speeds below , gusting winds might push the ship into the canal sides. In an emergency, the units could have been used to steer the ships at speeds under and, if the ships' main engines were rendered inoperable, could propel the vessel at a speed of in calm seas. When not in use, they were to be retracted into their vertical shafts and protected by water-tight covers.
Flight deck and hangars Flight deck The Graf Zeppelins steel flight deck, overlaid with wooden planking, was long by wide at its maximum. It had a slight round down right aft and overhung the main superstructure but not the stern; being supported by steel girders. At the bow, the carriers were to have an open forecastle and the leading edge of her flight deck was uneven (mainly due to the blunt ends of her catapult tracks), but it did not appear likely that would have caused any undue air turbulence. Careful wind-tunnel studies using models confirmed this, but they also revealed that their long low island structure would generate a vortex over the flight deck in these tests when the ship yawed to port. This was considered to be an acceptable hazard when conducting air operations.Brown, p. 10
Hangars The Graf Zeppelin class's upper and lower hangars were long and narrow with unarmored sides and ends. Workshops, stores and crew quarters were located outboard of the hangars, a design feature similar to that of British carriers. The upper hangar measured x ; the lower hangar x . The upper hangar had vertical clearance while the lower hangar had less headroom due to the ceiling braces. Total usable hangar space was with stowage for 43 aircraft: 20 Fieseler Fi 167 torpedo bombers, 18 in the lower hangar, two in the upper hangar; 13 Junkers Ju 87C 'Stuka' dive bombers in the upper hangar and 10 Messerschmitt Bf 109T fighters in the upper hangar.Breyer, p. 52
The Graf Zeppelin class had three electrically operated elevators positioned along the flight-deck's center-line: one near the bow, abreast the forward end of the island; one amidships; and one aft. They were octagonal in shape, measuring x , and were designed to transfer aircraft weighing up to 5.5 tons between decks.Whitley (1985), p. 155Breyer, p. 54
Flight deck Two Deutsche Werke compressed air-driven telescoping catapults were installed at the forward end of the flight deck for power-assisted launches. They were long and designed to accelerate a fighter to a speed of approximately and a bomber to .
A dual set of rails led back from the catapults to the forward and midship elevators. In the hangars, aircraft were to be hoisted by crane - a method also proposed for the Essex-class carriers of the United States Navy, but rejected as too time-consuming - onto collapsible launch trolleys. The aircraft/trolley combination would then be lifted to flight deck level on the elevator and trundled along the rails to the catapult start points. When the catapults were triggered, a burst of compressed air would propel moveable slideways within the catapult track wells forward.Wagner & Wilske, pp. 54–56
As each plane lifted off, its launch trolley would reach the end of the slideway but remain locked in place until the tow attachment cables were released. Once the slideways were retracted back into the catapult track wells and the tow cables unhooked, the launch trollies would be manually pushed forward onto recovery platforms, lowered to the forecastle on "B" deck, then rolled back into the upper hangar for re-use via a secondary set of rails. When not in use, the catapult tracks were to be covered with sheet metal fairings to protect them from harsh weather.