[MarkSheppard]

Originally Posted by RecruitMonty

The Flugdeckkreuzer are also interesting designs. I like the Mark A III and A IV especially.

The USN and other navies investigated the flying deck cruiser concept heavily during the 1920s up to February 1940; but it was killed off by the coming of WWII.

One such actual USN FDC Design of the 30s

The French investigated it as well, their final FDC warship having a single 11 inch gun turret aft.

French PA-5B

This is what

THE HYBRID WARSHIP
The Amalgamation of Big Guns and Aircraft

Has to say about the German FDCs:

The German Navy had taken a step toward the hybrid during the design of the carrier Graf Zeppelin. Because Germany was forbidden by the Treaty of Versailles from building aircraft carriers or military aircraft during the 1920s, German designs of the early 1930s were affected by the same factors that had influenced the carrier designs of other navies a decade earlier: fundamental inexperience in carrier operations and a belief that the vessel should be able to defend itself against surface ships. In 1933, when the carrier design process was initiated, it was thought that the ship would have to fight its way through a North Sea blockade; later, it was theorised that a carrier might serve as a surface raider, either accompanied by cruisers and battleships or alone. In the latter case it would function as a sort of super- Wolf, the aircraft-equipped mercantile menace of the First World War. To these ends, the early characteristics for Germany's first carrier, issued in March 1934, called for a 15,000 ton ship armed with either six 8in or nine 6in guns. Speed was to be 33 knots, and aircraft capacity was set at about 60.

Admiral Erich Raeder, Commander-in-Chief of the Kriegsmarine, was especially interested in providing these ships with firepower astern; he believed they would need guns aft to deter a pursuer. He probably saw the ship as a lone commerce raider; however, this battery proved impossible on the desired tonnage. Instead, eight 5.9in guns in armoured casemates were substituted; eventually, this battery grew to sixteen guns in twin casemates. These guns, useless against aircraft, were supplemented by a strong AA battery of 4.1 in guns. Since such weapons could have shot up unprotected merchantmen almost as well as the 5.9in guns, the heavier guns must have been intended to defend the ship against small warships. Nevertheless, it is difficult to understand why the single-purpose batteries were not merged into a uniform dual-purpose armament.

At this point, Adolf Hitler enters the story. The German dictator had shown a lifelong interest in big ships and their technology, sometimes drawing improbable battleship designs in his sketchbooks. As in so many other areas, his interest was sporadic and his comprehension of the topic incomplete; it often showed that peculiar combination of penetrating insight and impossible fantasising that characterised so much of his military thinking. So, shortly before Graf Zeppelin was launched, Hitler remarked that a well armed aircraft carrier would make an excellent commerce raider; he did not pursue this line of thought at the time, but he would return to it occasionally in the years ahead.

Graf Zeppelin was still incomplete when the Second World War broke out. The German Navy soon found itself in the uncomfortable position of having neither a substantial surface fleet nor an adequate submarine force; Hitler had promised Raeder that war with Britain would not come until the mid-1940s, so the navy had initiated a massive construction programme, the famous 'Z Plan', centred on powerful battleships. All this went into the scrap heap on 3 September 1939 when Britain declared war. Only those ships nearing completion were to be worked on; efforts would otherwise be concentrated on the construction of U-boats. By May 1940, work on Graf Zeppelin had come to a halt, even though the ship was more than 85 per cent complete. It was felt that the war would be brought to a successful conclusion before the end of the year, well before the carrier could be finished. When the hope of a quick victory passed, there were always other, more pressing concerns, and the carrier languished in a variety of Baltic ports until she was finally scuttled at Stettin to avoid her capture by the Soviets. Salvaged, she was taken under tow to Leningrad, but apparently foundered during the voyage, perhaps after striking a mine.

While Graf Zeppelin was towed from harbour to harbour, the German constructors, like their counterparts in the Service Technique, continued designing warships even though there was an ever-diminishing possibility of such ships ever being built. Most famous of these paper projects were the enlarged versions of the 'H' class battleships studied at Hitler's orders, which resulted in the giant H-42, H-43 and H-44 designs. Hitler's interests were not confined to battleships, however. In July 1940, he once again mentioned the commerce-raiding potential of 'cruisers equipped with flight decks' during a naval affairs conference with Raeder. In response, the navy's construction office suggested the conversion of one of the incomplete 'M' class light cruisers to carry about fourteen aircraft with some reduction in armament and speed. However, at 7800 tons standard displacement, these ships would clearly have made inadequate flight-deck cruisers.

Hitler probably expressed interest in hybrid ships on subsequent occasions, for in 1942 the Naval War Staff prepared a paper which specifically concluded that battleship-carrier hybrids were not feasible, since the aviation facilities would interfere with gunnery. A hybrid cruiser, on the other hand, was considered a much sounder proposition. The roles envisaged for such a vessel were exactly those advanced by American advocates of the flying-deck cruiser some twelve years earlier: scouting, air defence, convoy protection and commerce raiding. Admiral Raeder liked the idea sufficiently to order further study.

In the end, two series of hybrid designs emerged: small flight-deck cruisers {Flugdeckkreuzer), and much larger ships {Grossflugzeugkreuzer). The smaller designs were completed by 1943; all showed modest characteristics, as a glance at the table will show. Armed with four or eight 5.9in guns and carrying ten to twenty-five aircraft, they are in some ways less impressive than the American flying-deck cruiser designs of the 1930s. As in other German designs for aviation ships, the aircraft capacity seems relatively small compared with the size of the ships; this was probably the result of a tendency on the part of German designers to avoid sponsons and other projections from a ship's side, which meant that the AA guns and directors cut into the hull width available for the hangar; workshops and crew quarters surrounding the hangar may have reduced its potential volume as well. In all these flight-deck cruiser designs, the use of diesel or combined diesel/steam propulsion would have given the ships a considerable cruising radius — valuable for commerce raiding — at the cost of a heavier machinery plant.

These flight-deck cruisers, perhaps better classed as well armed carriers, might have functioned well as merchant raiders; the same cannot be said of the Grossflugzeugkreuzer designs. These enormous ships showed little appreciation for the operational needs of aircraft; moreover, their aircraft capacities were remarkably small for their size. They have been characterised by Wilhelm Hadeler, who had been in charge of the design of Graf Zeppelin, as 'sham assignments which were worked out to protect a small circle of younger employees from conscription'. However, Hadeler was not in the design office when these hybrids were sketched, and the surviving documentation on the projects is incomplete, so their exact origins remain obscure.

The series began with Design AII of 9 April 1942. This ship had a full load displacement of 40,000 tons, yet carried only twenty-three aircraft. Forward, there was a quadruple turret for 8in guns, a battery that seems very light both in number and calibre; the drawing shows a turret similar in size to the quadruple 11in turret of the later A IV design, so it may be that the calibre given with this drawing was in error. This supposition gains some support from the fact that an undated variation on this design, AII*, apparently was to be armed with six 11in guns in two triple turrets on about the same displacement as A II; it seems unlikely that a greater number of guns far larger than 8in could have been substituted without considerably increasing the displacement. The quadruple turret may have been inspired by a review of the French design materials that had fallen into German hands in the summer of 1940. In other respects, A II shows features that would be shared by the subsequent designs in the series: a heavy 5.9in battery in twin casemates, a 4.1in AA battery located along the sidedecks, a narrow hangar, AA directors projecting dangerously above the level of the flight deck for no apparent reason, and a portside island. This last feature has no explanation. Propulsion was to be pure diesel, with the exhaust to be vented via outlets along the ship's side; as in the subsequent designs, a speed of 34 knots was anticipated. The most unusual feature of this sketch is the extreme flare of the bows, which surely would have subjected the ship's structure to severe pounding in any sort of a seaway.

AII was followed by A III; this called for a ship of no less than 70,000 tons, yet it carried only thirty-two aircraft and had a battery of six 11 in guns in two triple turrets forward. Its tremendous displacement is explained in part by the heavy protection specified; side armour consisted of a 9.8in belt, while the flight deck was almost 2in thick and an armoured deck was 5.9in. This design was to be driven by a combined steam/diesel plant and so shows a funnel, which seems rather short; most carrier funnels were high to get the hot gases as far above the flight deck as possible. The forward end of the flight deck, as Hadeler says, 'appears to have been laid out specifically to cause turbulence'. Worse still, the height of the second 11 in turret was such that the catapults had to be angled off the centreline so that aircraft could clear it, which would have made rapid launching of aircraft impossible. The ship would have had to zig-zag wildly to get first one, then the other, catapult into the wind. Combined with all its other faults and weaknesses, it seems a very poor effort indeed, and demonstrates a lack of understanding of even the most basic requirements of shipboard aviation.

A IV offered some improvements. Again, the ship was 70,000 tons, with protection somewhat reduced from that of A III. The battery was concentrated in a single quadruple 11 in turret forward, which allowed a reduction in the height of the hangar; more importantly, the two catapults could now be placed parallel to the axis of the ship, greatly facilitating aviation operations. Propulsion was pure diesel, the increased weight of which may account in part for the reduced level of protection. Aircraft capacity was again a paltry thirty-two machines.

The final design in the series, Project A IIa, was the worst of a bad lot. Another 70,000 tonner, it showed all the worst features of its predecessors and added the final lunacy of a centreline superstructure. The draughtsman tried to ameliorate this retrograde ediface with a half-hearted attempt at streamlining, but the typical German tower-mast structure with its attendant platforms and directors would surely have created almost as much turbulence as had Furious' upperworks. The catapults are once again angled outboard, the periphery of the flight deck cluttered with AA directors.

No drawings seem to have survived for a final undated design, designated C. This is unfortunate, for it shows a completely different mix of features from the other designs. It was armed with six 11in guns and featured protection as heavy as that of the other designs, and a diesel/ steam propulsion plant good for 34 knots. Unlike the other designs, however, it was to carry no fewer than eighty aircraft, a complement befitting its 56,000 ton size. How this was to be accomplished is not known; perhaps the AA battery was finally sponsoned out from the hull proper, allowing an increase in hangar width; or perhaps a permanent deck park was employed. Whatever its arrangements may have been, it is the only design in the series that seems anywhere near adequate.