Design A-150 battleship

Artist's impression of an A-150-class battleship
Class overview
Name	A-150
Builders	Yokosuka Naval Arsenal Kure Naval Arsenal
Operators	Imperial Japanese Navy
Preceded by	Yamato class
Succeeded by	None
Planned	2
Completed	0
Cancelled	2
General characteristics
Type	Battleship
Displacement	Approximately 70,000 long tons (71,000 t)
Length	263 m (862 ft 10 in) (est.)
Beam	38.9 m (127 ft 7 in) (est.)
Propulsion	Unknown
Armament	3 × twin 51 cm (20.1 in) guns "Many" 10 cm (3.9 in) dual-purpose guns
Armor	Possibly a 45.7 cm (18 in) side belt

Design A-150, popularly known as the Super Yamato class, was a planned class of battleships for the Imperial Japanese Navy. In keeping with longstanding Japanese naval strategy, the A-150s would have carried six 51-centimeter (20.1 in) guns to ensure their qualitative superiority over any other battleship they might face. These would have been the largest guns ever carried aboard a capital ship.

Design work on the A-150s began after the preceding Yamato class in 1938–1939 and was mostly finished by early 1941, when the Japanese began focusing on aircraft carriers and other smaller warships in preparation for the coming conflict. No A-150 would ever be laid down, and many details of the class' design were destroyed near the end of the war.

Background and Design

See also: Empire of Japan during the Later Shōwa period

In the 1930s, the Japanese government began a shift towards an ultranationalist militancy. Planners envisioned an empire stretching from Japan to the resource-rich European colonies in Southeast Asia, and defensible islands in the Pacific Ocean (the Greater East Asia Co-Prosperity Sphere). The extensive distances involved, and the likelihood of this expansion leading to a confrontation with the United States, led the Japanese to build and maintain a large fleet that could seize and hold onto these territories. The U.S. posed a particular problem for Japan, as it possessed significantly greater industrial power, and several leading members of the United States Congress had pledged "to outbuild Japan three to one in a naval race".

The Imperial Japanese Navy had recognized since at least 1896 that the country could not outproduce its potential opponents, and therefore insisted that its ships had to be more powerful than foreign equivalents. It established this qualitative lead at various times over the next 40 years, with the Kongo-class battlecruisers just before World War I, the Nagato-class battleships at the end of that war, and the Yamato-class battleships in the 1930s. The A-150s were designed according to that doctrine to continue their qualitative superiority in battleships over their most likely opponents, the United States and Great Britain.

Early Drafts

After the design process finished with an Improved A-140F6 variant design slated for Shinano and Warship No. 111 (see: Yamato Class) of the 4th Programme, there was a new design effort in 1938/1939 to have a new heavier Yamato-class variant that mounted 8-9 of the 510 mm (20.1 in) guns and be protected from the same weapon at a range of 20-30km. The Japanese Admiralty preferred the twin gun turret designs due to its larger space for both guns (decreasing reload times), smaller turrets for a slimmer profile and also reports of higher accuracy from dual gun turrets. Also, the 510mm (20.1 in) inch gun had already been developed and produced in 1935 for trials involving both the 460mm (18.1 in) guns mounted to Yamato and the future 510mm (20.1 in) Naval Guns. This design (A-150) was originally part of the 6th Programme that the late designer Fujimoto conceived in 1934 and the other designers followed in the Yamato Project (A-140) of the mid 1930s (even following his death), however it became its own project during its development until focus shifted to further improving the Yamato Class.

The Admiralty pushed for a 30 knot top speed initially; however it was feared that due to the main gun size and sheer weight of the turrets, it would increase displacement up to 100,000 tons. A lot of mounting options were considered including triple mount turrets of 510 mm (20.1 in) or even quadruple mounts. Although quadruple mounts were impressive on paper, it proved to be too much as the increase in displacement (way beyond the bounds of 100,000 tons) and decrease in speed (less than 27 knots) made it much more impractical. In the end, before the end of World War II, two designs were considered, a variant with four dual mount 510 mm (20.1 in) guns and a speed of 27 knots at 85,000 tons and a final sub-variant of the previous that could cruise along at 30 knots at 100,000 tons. Secondary Armament on the ships varied as to whether or not they would retain the 2 triple 155mm (6.1 in) guns of the Improved A-140F6 design slated for Shinano and Warship No. 111. No definitive answer was reached however before the project shifted in goal. Although general characteristics were vague on how many 100 mm (3.9 in) 60 Caliber guns were mounted, many artist drawings, in reference to plans of Shinano and Warship 111 (Improved A-140F6), called for 12-16 dual mount 100 mm (3.9 in) 60 Caliber guns with 6-8 per side between the main tower and secondary tower. It was also possible that they would mount many dual mount 25 mm (1.0 in) AA cannons (at least 36 dual mounts that were present on the Improved A-140F6 design for Shinano).

Number of Ships and Impracticality

It was proposed that 4 ships would be built in this class, however in the meantime, during World War II; multiple things happened that closed the door on this design project forever. Not only would the fourth hull of the Yamato class be broken up and reused for other construction projects as well as Shinano (the third ship of the Yamato class) was converted into an Aircraft Carrier, but also the 4 ships of this class were never ordered. The sobering truth was that the Yamato class as built and in her 1945 configuration after her refit were pushing the limits of Japanese Industry and drydock capacity as the Super Yamato designs would need a new slipway even larger and longer than Yamato and her sisters. In fact, the sheer size of the A-150 design would be impossible to construct very quickly with the quality of steel the Japanese had that would be required for a ship of the A-150’s size and weight. It was also rumored that armor plates would have to be attached in layers in order to achieve the desired thickness on some surfaces. There were many concerns about the cost of these massive ships and also fears that the Imperial Diet would reject such overly large and expensive designs.

Design Shift and Cancellation

With this in mind, the Design Department and Admiralty refocused their efforts on improving the existing A-140F6 design (Yamato) beyond what was already slated for the variant intended for Shinano and Warship No. 111 of the 4th Programme, keeping to the existing dimensions of Yamato, Musashi and Shinano instead of bigger designs and just replacing the 9 460mm (18.1 in) guns in triple turrets with 6 510mm (20.1 in) guns in dual mount turrets. In a way the A-150 plan was, in its final form, an Improved Design of Shinano slated for the 5th Programme to be built in 1942 with 6 510 mm (20.1 in) guns in dual mounts and 12 dual turrets of 100 mm (3.9 in) guns; retaining the triple 155 mm (6.1 in) guns forward and aft of the superstructure. The loss of Yamato and Musashi, along with the Admiralty’s switching of priorities to Aircraft Carrier Production (as evidenced by Shinano's Conversion into an Aircraft Carrier) instead of Battleship Construction halted all progress on any further Yamato Class Battleships and their future variants including the A-150 Project.

Specifications

Plans for the A-150s were finished in early 1941 (Post project shift to further improve the Shinano and Warship No. 111 design for the next 5th Programme), for most intents and purposes. However, these were destroyed at the end of the war, along with most of the other documentation relating to the class. The general destruction of records and Japan's extensive efforts (before and during the war) to keep any information about the ships out of the hands of foreign nations severely limited the amount of information on the ships available to historians. For these reasons the A-150's exact specifications are uncertain. The displacement in some sources was rumored to be similar to the Yamato class, which was around 70,000 metric tons (69,000 long tons), In reality it might have been propaganda to throw allied intelligence off about the new ships like they did for the Yamato Class (Project A-140), or otherwise in reference to the new focus for an improvement to the existing Yamato class battleships being built or already in service. More modern sources compiled from the designers' accounts of the project put the tonnage (before the switch in focus) to a range between 85,000 metric tons (84,000 long tons) and 100,000 metric tons (98,000 long tons). As these are theoretical numbers from never built designs, the actual tonnage may have been close to 150,000 metric tons (150,000 long tons) had they been built. The belt armor was rumored to be 45.7 centimetres (18 in) thick, however this might be a number more intended for the 5th Programme after the design focus shifted or otherwise a fictitious number. What is known is that the Turret Faces were to be 800 mm (31.5 in) thick while their roofs 295 mm (11.6 in) thick. The displacement and the high armor thickness was so much of a problem for Japanese industry at the time that steel mills in Japan were incapable of manufacturing it in one piece. Instead, multiple layers of armor plates would have been used, despite its reduced effectiveness as compared to a single plate of the same total thickness. Speed rumors range between 27 knots of the original Yamato Class to over 30 knots, however this confusion is mainly due to the priority shift in the project midway through development and the realized impracticality of such a large design. Although no powerplant is known for certain, it is probably safe to assume the A-150 Variants would be powered by Steam Turbines like Yamato and her sisters. Although hybrid Turbine/Diesel or full diesel arrangements were explored in the A-140 Yamato Project, it was discovered that the Marine Diesel Engines produced domestically were less powerful and less reliable than initially thought. This spurred the push to have the Yamato be powered fully by a Steam Turbine Powerplant which would have most likely not changed by the time of the A-150 design's construction.

Armament

The design of the A-150s called for a main battery of between eight and nine 45-caliber 51-centimeter (20.1 inch) guns in four twin or triple turrets. Later, after the project shifted in focus to improve the Shinano Class (4th Programme) for the 5th Programme (Set to be constructed in 1942), this number was reduced to 6 51-centimeter (20.1 inch) in three twin turrets. These would have been the largest ever fitted to a capital ship, dwarfing the 46-centimeter guns mounted on the Yamato class, and were a key factor in historians William H. Garzke and Robert O. Dulin's argument that the A-150s would have been the "most powerful battleships in history". By 1941, one—possibly two—of the 51-centimeter guns were being constructed at the Kure Naval Arsenal and detailed designs of their turrets were drawn up. The turrets would have weighed 2,780 metric tons (2,740 long tons) and each gun would have massed 227 metric tons (223 long tons). They would have had a total length of 23.56 meters (77 ft 4 in) and the bore length was to have been around 22.84 meters (74 ft 11 in). The armor-piercing shells would have weighed 1,950 kg (4,300 lb). After priority shifted to the improved A-140F6 slated for the 5th Programme after discovering the impracticality of the higher tonnage designs, the new plan called for this replacement (9x3 18.1 inch guns to 6x2 20.1 inch guns) to be carried out as a refit on all Yamato Class ships currently in service and mounted to all future ships starting with Warship Number 797 or 798 (the two ships slated to have their keels laid in 1942 after Shinano and Warship No. 111 as the 5th Programme).

The composition of the A-150's secondary armament is not fully known. Historians Eric Lacroix and Linton Wells have written that Japanese designers were considering mounting a large number of 65-caliber 10-centimeter (3.9 in) Type 98 dual-purpose guns, though this was not final. These guns had a maximum elevation of +90°, which gave them an effective ceiling of 11,000 meters (12,030 yd) and a horizontal range of 14,000 meters (15,311 yd). They fired 13-kilogram (29 lb) projectiles at a muzzle velocity of 1,030 m/s (3,400 ft/s), although resulting wear on the barrels reduced their designed lifespan to only about 350 rounds. They were able to fire 15–19 rounds per minute. Many artist interpretations show 12-16 of these guns mounted as part of either the original large tonnage designs before the shift to further upgrade the Yamato Class when priority shifted. The 12 65-caliber 10-centimeter (3.9 in) Type 98 dual-purpose guns was already slated for the Improved A-140F6 design which was intended for Shinano when she was built. This switch was a 1 to 1 switch from 12 of the 127mm or 5 inch twin mounts of the Yamato and Musashi 1944/1945 design respectively to 12 65-caliber 10-centimeter (3.9 in) Type 98 dual-purpose guns. Although the 5th Programme and the previous 4th Programme (improved variant for Shinano and Warship No. 111) did keep the remaining 2 triple 155 mm (6.1 in) guns, commonly available on Japanese light cruisers, whether they would have ended up being mounted to the A-150 designs of the 6th Programme is in heavy speculation. The reason why the Japanese might have wanted to omit them from the design was that the guns were poorly armored and only capable of protecting the crew from shell splinters due to being 25mm or around 1 inch thick all around. In fact, the Improved A-140F6 variant design, intended for Shinano and Warship No. 111 during their initial construction, called for an extra 25mm to be added to increase the protection to around 2 inches or 50mm as these turrets were plucked directly off of former Japanese Light Cruisers that were rearmed as Heavy Cruisers. Some artist interpretations have the 25mm AA turrets from Yamato in dual mounts represented (at least 36 of those turrets as intended for the Shinano Subvariant Design); while others have them removed completely. In reality, many nations, including Japan studied and found out that the 20mm variants of anti-aircraft weapons were too short range and generally insufficient to shoot down aircraft as the war progressed. As such, many nations explored adding more weapons closer to 40mm that could blow most planes out of the sky in only a few hits.

Construction

As war with the United States became increasingly likely over the Second Sino-Japanese War, and particularly after the Japanese seizure of French Indochina in mid-1940, all design work on battleships was diverted in early 1941—even though the A-150's design was nearly complete—in order to focus on higher-priority warships like aircraft carriers and cruisers. None of the A-150s were ordered, however two ships of the 5th Programme (After the Improved Shinano design was finalized for the A-150 Program), provisionally designated as Warships Number 797 and 798, were projected in a 1942 building program. Under this plan, 797 would have been built in the same dock as Shinano, while 798 would be built in Kure in the same dock as Yamato after a fourth Yamato-class ship was launched (Warship No. 111). The ships would have then have been finished in 1946–1947, but the war's turn against the Japanese after the Battle of Midway meant that the need for ships other than battleships never abated.

Bibliography

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• Lacroix, Eric & Wells, Linton (1997). Japanese Cruisers of the Pacific War. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-311-3.
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Further reading

• Lengerer, Hans & Ahlberg, Lars (2019). Battleship Tosa Demolition Tests to the Modified Yamato Class. Capital Ships of the Imperial Japanese Navy, 1868–1945. Vol. 3. Zagreb: Despot Infinitus. ISBN 978-953-8218-57-6.