German WW1 and WW2 carrier projects

Sooo.... Let's return to the beginning:

Project Ausonia, Flugzeugdampfer I

History
Since the beginning of the war, aircraft had gained more and more in importance as technology advanced as well. In regards to the war at sea, aircraft had taken over mostly reconnaissance roles, but also bombing assaults. Naturally, only seaplanes could be used for obvious reasons. Since the beginning of the war, both sides experimented with ship-borne aircraft, to increase the operational range and to protect and support ships operating far from home. Those seaplane motherships included modified freighters and ferries, like the German Answald or the British Ben-my-Cree. Aside from that, onboard aircraft also made an appearance on other ship types, like cruisers, destroyers or u-boats.

The surprise came for the Germans on June 10th, 1918, when they first became aware to the existence of a mothership for land aircraft – the aircraft carrier HMS Furious. Bombers on patrol engaged the carrier and her escorting three destroyers, but came under heavy flak fire and were driven away by onboard aircraft (relative correctly, the pilots and analysts suspected a modified British armored cruiser or American battleship, but had had drastically overestimated the size, guessing 200-240m in length)

The Germans had also learned the value of their own aircraft carrying ships: Dedicated motherships had the size and installations to serve and supply several seaplanes, but were too slow to keep up with the fighting fleet. Meanwhile the cruiser-carrier Stuttgart was fast enough for fleet duty and very much capable in seaplane deployment, but lacked in size and aircraft numbers. Meanwhile the naval air arm was gathering every available piece of information on aircraft motherships, to be used after the war.
But some couldn’t wait, and that included higher-ups like Admiral Scheer himself. With the progress of the war, more and more minefield had to be cleared, often ever further away from the German coast. To secure the minesweeping ships in one operation, three seaplane carriers would be needed: Two on escort duty, one in reserve. One Cruiser-carriers would operate further out as pickets or u-boat escorts, the other one would be on stand-by or fleet duty. The Roon conversion was a result of these plans.
Ideally, each seaplane mothership would need a top speed of 15 kn and should carry 6 or more planes – none of the German motherships in service were capable of that, so plans were made in September 1918 to convert the two Barbarossa-class liners Bremen and Königin Luise (both of 1897).

The appearance of land aircraft on the sea changed those plans. Superior to regular seaplanes, the British heavily disrupted the German aerial reconnaissance and consequently naval operations themselves. With German minesweeping on the back foot, the British naturally stepped up their own mine laying activities. Only the arrival of more powerful German seaplanes stopped the British dominance. As such, demands were made to speed up the conversions of Bremen and Königin Luise and include land aircraft capabilities as well. If land aircraft couldn’t be included, a dedicated ship would be needed – the Ausonia. Simultaneously, training and testing for aircraft carrier operation would begin at either Danzig-Langfuhr or Warnemünde. Lt. Dr.-Ing Jürgen Reimpell would be assigned to this project due to his design work on Ausonia.

In September 1918 Jürgen Reimpell’s proposal was circulated around the higher levels of the German Navy, not only for the purpose of converting the Ausonia, but maybe even incorporating certain design features in other ships, namely the Bremen and Königin Luise mentioned before. The upper brass was impressed by Reimpell’s proposal, but the ultimate decision would be made later.

On October 8th, 1918, the conversion of Bremen and Königin Luise was rejected: Both ships had too little protected and too much of a peace-time value. The Roon conversion was rejected due to the long construction time (12 months starting in January 1919) and that it would draw men and material away from u-boat construction. Ausonia was rejected for the same reasons as Roon. Additionally, Ausonia would still have the same weaknesses of a civilan ship after conversion, the same drawback that spelled the doom for the reconstruction of the liners above.

Instead, it was decided to equip all Sperrbrecher-type mine warfare ships with aircraft facilities. Trials for necessary facilities of an aircraft mothership, however would continue.

Design
In his proposal Reimpell lists all the advantages of having land aircraft on sea, the threat of the British carrier and the measures necessary for a German carrier program.
Additional programs:

In addition to building a carrier itself, the necessary training and testing infrastructure would have to be established. That required the training of pilots, the evaluation of new equipment, like arrestor gear, transport- and conveyor measures and the selection of suitable aircraft, but also wind conditions and the form and shape of the landing strip. Trials could, for example, conducted on a lake near an aircraft yard, using a barge(s) as training carrier. Additionally, construction of airplanes with foldable wings should begin immediately, as other nations had already such types in service. Stowing plans attached to the paper clearly showed the advantage that such a type would bring.

Selection of ships:
Obviously, a larger and longer ship would be better suited than a smaller one. The longer ship, the better, as a longer runway could be installed. A speed of 12kn was required for coastal operations, 15-17 kn for mine ship escort and 19-21 kn for fleet operations.

Building a new ship would take too long and the experience for such ships was simply not there.
Rebuilding an existing seaplane mothership would not work, as none fulfilled the required criteria in size and speed.
Converting an existing warship would work, but with only a few of the required size available, none could be spared.
Converting a finished fast ocean liner would once again take too long (the entire superstructure would have to be removed and their protection was relatively weak.
Consequently, converting a half-finished ship would be the best solution. Reimpell suggested three suitable ships: SMS Graf Spee (Mackensen-class), SS Bismarck (later RMS Majestic) and SS Ausonia. While the first two would be better suited, Reimpell focused his work on Ausonia, as the ship would be the most likely ship to be available.

Ausonia had been ordered by the Italian Sitmar Lines at Blohm & Voss yards before the outbreak of the war in 1914. Naturally, the outbreak prevented her delivery, but the hull was nonetheless launched on April 4th, 1915. Construction had progressed so far that the hull of the ship had been completed up to deck one and most of the machinery had already been installed. To shorten the conversion time, all of Reimpell’s proposals saw minimum modifications, if at all, to the already existing ship body.

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Blohm & Voss had not been lazy either. With an unused hull in the harbor, the company had their own ideas of what to do with it. In his proposal Reimpell included a plan to convert the Ausonia into an auxiliary cruiser. For this, the ship would only be completed in a most basic way, not the way originally intended. As armament, Blohm & Voss planned for four 150mm guns mounted in four single mounts on the centerline and six 105mm single guns, three per broadside. The drawings show the 150mm guns in unique mounts, as displayed on the drawing, although due to the nature of a quick wartime conversion, it would be unlikely that she would carry anything else but guns already in production. Additionally, there would be room for up to 250 or 400 mines (drawings and documents differ) with deployment chutes at the back (this room could also be used for additional coal, if needed).

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Modifications:
The lower decks of the auxiliary cruiser variant housed the boilers and machines as well as coal bunkers. Crew quarters, storage and the mines. Those would be left unchanged in the carrier conversion. The mines would be left onboard; in fact, if necessary, the seaplanes should be switched for additional mines, to have the ship serve as a minelayer.

All proposals had a lower seaplane hall and an upper land aircraft hall. Located in the forward lower hall was a small repair shop for aircraft. More extensive maintenance facilities were not needed, as those would be located on land and the ship was not meant for long missions. In front of the lower hall, below the runway were officer quarters and storage. cranes were the preferred method of transportation and deployment, as those had been proven in operation on other seaplane motherships.

The upper hall housed the land aircraft and opened to the runway. At the back were quarters of the commander. On top of the hall was of course the landing strip. With a length of around 50m (in all proposals), a speed of 20 kn and headwind, it was enough for the land aircraft to take off, but Reimpell also adds that extensive trial would be required, to determine the final form and length of the runway.

According to Reimpell, horizontal light was important for aircraft maintenance, hence the long row of windows that lined both halls. The doors were designed big enough to handle the largest of all available German airplanes that could be carried. As closure, either tarpaulin (as depicted) or sliding doors would work.

Any concentration on larger armament would draw away space from the ship’s intended role to carry aircraft. As such, medium and heavy artillery were not suitable, only light guns and/or flak should be considered. In all proposals there was room for such weapons next to the officers’ quarters below the starting runway. In proposals 2 & 3 could also have weapons on the upper deck on starboard or at the end of the landing runway. The shipbucket drawings show a standard 88mm flak as a weapon of choice.

According to Blohm & Voss, the conversation would only take 8 month (opposed to the 12 months later documents mention), requiring 500-600 workers and the same priority as u-boat construction.

In design no. I the funnels were trunked together and moved as far forward as possible. Bridge and mast were then moved as close to the funnel as possible. Air ducts did not end on deck but in the side of the ship. Although this arrangement had certain disadvantages, it allowed for as large a runway as possible. The centerline arrangement however still caused a split in the aircraft halls and reduced the landing runway to only 105m.

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The second proposal extended the landing strip to 130m, by moving bridge, mast and funnel to starboard. A second mast with another crane was added on port. According to Blohm & Voss the asymmetrical arrangement would not influence the stability of the ship. The arrangement of the masts naturally made it dangerous for planes who had failed the landing. The arrangement of the masts is somewhat strange: In the accompanying drawings, the higher mast is shown on starboard, with the longer crane clearly connecting to it. However, the top view clearly places the longer crane on the port side, which is where it is put on the drawing.

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To eliminate the danger of the two masts, proposal no. III moved everything completely to starboard and extended the landing strip further forward, to a maximum length of 155m. At this point, the stabilization beams would extend to far above the ship’s width to still leave room for the blow starting airplanes. The entire superstructure was slightly elongated as well and slimmed down at the same time.By moving everything to starboard, another additional gate for seaplanes was needed to still allow for the transfer of land airplanes to the workshop in the hall below.

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Of course it would be ideal to reduce the entire superstructure altogether. For future development Reimpell therefore suggested to eliminate masts and funnel in a future, dedicated land aircraft carrier, to make operations, and therefore training, a lot easier. This would be achieved by switching propulsion from coal to oil or diesel.

General Technical data

Length: 156 m (waterline; for some reasons Gröner and other later documents only give a waterline length of 149,6 m)
Width: 18,8 m
Draught: 7,46 m (as liner), 8 m (as auxiliary cruiser)
Engines: 10 boilers and 2 set of double-stage turbines for an average of 13000 shp or short-time maximum of 22000 shp – two shafts
Range: 23800 nm / 12 kn; 13600 nm / 17 kn; 9600 nm / 20 kn (as liner)
Speed: 20 kn or short-time burst of 22 kn (as liner)
Displacement: 12600 t (as liner), 13800 t (as auxiliary cruiser)
Weapons:
As auxiliary cruiser:
4 x 150mm guns in single mounts
6 x 105 mm SK/L40 in single mounts
250 or 400 mines

As aircraft carrier:
Light guns and/or flak guns (depicted: 2-3 x 88 SK L/45 C/13 Flak in single mounts MPL C/13)
250 or 400 mines (if required by mission)
Aircraft:
10 land aircraft (depicted: Fokker D.VII)
13 fixed-wing seaplanes (depicted: Friedrichshafen FF.49C) or 19 fold-wing seaplanes (theoretical 200 hp CHFT-type)

The next piece might be so obscure it probably won't count...

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