Japan Designed Battleships With Monster 20-Inch Guns. Why Were They Never Built?

 In EPC, UK, Sea, Japan, FVEY, P5

Key Point: Had the war not come, Japan still would have bank­rupt­ed itself spend­ing on these mas­sive ships.

In January 1936 Japan announced its inten­tion to with­draw from the London Naval Treaty, accus­ing both the United States and the United Kingdom of nego­ti­at­ing in bad faith. The Japanese sought formal equal­i­ty in naval con­struc­tion limits, some­thing that the Western powers would not give. In the wake of this with­draw­al, Japanese bat­tle­ship archi­tects threw them­selves into the design of new ves­sels. The first class to emerge were the 18.1‑inch-gun-carrying Yamatos, the largest bat­tle­ships ever con­struct­ed. However, the Yamatos were by no means the end of Japanese ambi­tions. The Imperial Japanese Navy (IJN) planned to build anoth­er, larger class of super bat­tle­ships, and had vague plans for even larger ships to suc­ceed that class. War inter­ced­ed, but had Japan car­ried out its plans it might have deployed mon­ster bat­tle­ships nearly as large as super­car­ri­ers into the Pacific.

“Super” Yamatos

The A‑150 class would have super­seded the Yamatos, build­ing on expe­ri­ence with that class to pro­duce a more for­mi­da­ble, flex­i­ble fight­ing unit. Along with the Yamatos, these ships were expect­ed to pro­vide the IJN with an unbeat­able battle line to pro­tect its Pacific pos­ses­sions, along with newly acquired ter­ri­to­ries in Southeast Asia and China.

The A‑150s would the­o­ret­i­cal­ly have car­ried six 510-mil­lime­ter (twenty-inch) guns in three twin tur­rets, although if prob­lems had devel­oped in the con­struc­tion of that gun they could have car­ried the same main arma­ment as the Yamatos. The 510-mil­lime­ter guns would have wreaked havoc on any exist­ing (or planned) American or British bat­tle­ships, but would also have caused sub­stan­tial blast issues for the more del­i­cate parts of the ship. The A‑150s would have car­ried heav­ier armor than their small­er cousins, more than suf­fi­cient to pro­tect from the heav­i­est weapons in the American or British arse­nals. The sec­ondary arma­ment would have includ­ed a sub­stan­tial number of 3.9‑inch dual-pur­pose guns, a rel­a­tive­ly small cal­iber sug­gest­ing that the A‑150s may have relied on sup­port ves­sels to pro­tect them from enemy cruis­ers and destroy­ers.

Design com­pro­mis­es lim­it­ed the effec­tive­ness of the Yamatos by reduc­ing their speed and range; they could not keep up with the fastest IJN car­ri­ers, and burned too much fuel for eco­nom­ic employ­ment in cam­paigns such as Guadalcanal. The A‑150s would likely have been some­what faster (thirty knots) than the Yamatos, with a longer range more suit­able for mis­sions deep into the Pacific.

The con­struc­tion of the Yamatos chal­lenged the capac­i­ty of the Japanese steel and ship­build­ing indus­tries, and the A‑150s would have strained them even more. For exam­ple, pro­duc­ing the armor plate nec­es­sary to pro­tect a bat­tle­ship against twenty-inch guns was simply beyond Japan’s indus­tri­al capac­i­ty, and would have required seri­ous com­pro­mis­es. Moreover, the IJN would have strug­gled to sur­round the A150s with sup­port units. While the USN com­mit­ted to build­ing an enor­mous number of heavy cruis­ers, light cruis­ers and air­craft car­ri­ers in addi­tion to the bat­tle­ship fleet, Japan com­plet­ed only a small hand­ful of these ships during the war.

Little is known about the successors to the A-150 class, which would have been larger, faster and more heav­i­ly armed. Potentially dis­plac­ing a hun­dred thou­sand tons, and car­ry­ing eight twenty-inch guns in four twin tur­rets, even the con­tem­pla­tion of such ships would have required a seri­ous revi­sion of eco­nom­ic real­i­ties in East Asia. In any case, the changes in naval tech­nol­o­gy that ren­dered the bat­tle­ship obso­lete likely would have become obvi­ous before any of these mon­sters had entered ser­vice.

Strategic and Economic Folly

Japan ordered two A‑150 bat­tle­ships in the 1942 con­struc­tion pro­gram. The first would have suc­ceed­ed HIJMS Shinano on the dock; the second, the never named fourth sister of the Yamato class. However, wartime demands for small­er ships (and even­tu­al­ly for air­craft car­ri­ers) meant that nei­ther ship was ever laid down.

But the war only exposed under­ly­ing eco­nom­ic real­i­ties; it did not forge them. Japan barely had the indus­tri­al capac­i­ty to build the ini­tial Yamatos, along with all of the sup­port ships that the bat­tle­fleet would require. This is the dirty little secret of the entire Washington Naval Treaty system; the United Kingdom could out­pace Japanese con­struc­tion by a wide margin, and the United States could out­pace both com­bined, if it decid­ed to do so. The treaty system pre­vent­ed an arms race that Japan could not pos­si­bly have won, whether in 1921 or in 1937. Japan’s GDP at the begin­ning of World War II was a bit over half that of Britain’s, and less than a quar­ter that of the United States.

Japan’s naval suc­cess at the begin­ning of the Pacific War hap­pened because of the treaties, not despite them. The IJN played a poor hand very well, but in any kind of extend­ed naval com­pe­ti­tion against the United States, the UK, or a com­bi­na­tion of the two, it could not win. Upon dis­cov­er­ing the exis­tence of these ships, the United States would have begun to con­struct even larger bat­tle­ships, as well as other means of sink­ing large bat­tle­ships. Indeed, in 1952 the United States laid down USS Forrestal, the first of a class of four air­craft car­ri­ers sub­stan­tial­ly larger than the A‑150 class bat­tle­ships.


Had the war not come, Japan would have bank­rupt­ed itself spend­ing on these mas­sive ships. Japan lacked the indus­tri­al capac­i­ty to com­pete with the United States; indeed, even if it had man­aged to seize and keep wide swaths of East Asia, it could not have matched U.S. indus­tri­al pro­duc­tion for decades. The United States would have respond­ed to Japanese con­struc­tion with even larger, more deadly ships, and of course even­tu­al­ly with sub­marines, air­craft and guided mis­siles.

Warships are (imper­fect) reflec­tions of exist­ing eco­nom­ic real­i­ties. Timing, tech­nol­o­gy and grand strat­e­gy matter, but in raw com­pe­ti­tion involv­ing mature tech­nolo­gies, supe­ri­or eco­nom­ic strength will even­tu­al­ly pre­vail. The Japanese econ­o­my would even­tu­al­ly become com­pet­i­tive with that of the UK, and even the United States, but this would only happen in con­text of an open trad­ing system with access to the European and American mar­kets. No bat­tle­ship could carry guns large enough to bring that out­come about.

Robert Farley, a fre­quent con­trib­u­tor to TNI, is author of The Battleship Book. He serves as a Senior Lecturer at the Patterson School of Diplomacy and International Commerce at the University of Kentucky. His work includes mil­i­tary doc­trine, nation­al secu­ri­ty, and mar­itime affairs. He blogs at Lawyers, Guns and Money and Information Dissemination and The Diplomat.

This arti­cle first appeared in 2016.

Image: Wikimedia Commons

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