In 1942, Nakajima Chikuhei wrote "Winning game plan" and proposed the "Z -plane", a large long-range strategic bomber that could fly to Europe after bombing the US mainland and land in Nazi Germany or its occupied territories. This Z-plane, which Nakajima Aircraft Company designed, became the basis for the Fugaku.
On May 31, 1943, Nakajima explained the following plan at a dinner party at the Naval General Staff's official residence:
"By 1945, a large number of B-29 bombers will be deployed, destroying Japan's munitions factories and rendering it unable to fight. To prevent this, we will quickly design and build an ultra-long-range bomber to bomb the US mainland."
Nakajima is said to have presented his plan to Prime Minister Hideki Tojo, as well as the Ministers of the Army and Navy, and other related parties.
On August 15 of the same year, the Army Department of the Imperial General Headquarters sent a request to the Ministry of the Army for the "devising of a decisive weapon to complete the world war," which included an item on the list called for an "ultra-long-range airplane."
After this, the plan was approved by a joint planning committee of the Army and Navy, and the development of an ultra-long-range bomber named Fugaku was carried out with the participation of the Ministry of Munitions. However, the Army and Navy had different requirements, which made it difficult to make adjustments, and the Ministry of Munitions had Kawanishi Aircraft independently create a design proposal midway through, and there was strong opposition not only from the Army and Navy and other companies, but even within Nakajima Aircraft, so there were many problems with the development system. The first plan was for six Ha-54 engines , but the development of a new type of air-cooled quadruple radial engine took time, so as a temporary measure, the plan was tentatively carried out with six Ha-44 (air-cooled double radial type 18 cylinders, 2,450 horsepower/2,800 rpm) and Ha-50 (air-cooled double radial type 22 cylinders, 3,100 horsepower/2,400 rpm). As a result, the bomb load was reduced from 20 tons to 15 tons.
In 1943, construction of an assembly plant for the Fugaku began within the Nakajima Aircraft Mitaka Research Center. However, on April 28, 1944, the Japanese military gathered the relevant parties from the Army and Navy, the Ministry of Munitions, and related manufacturing companies to consider whether to continue research on the super-heavy bomber "Fugaku." As a result, if the Fugaku was produced as planned, it was expected that the Japanese Army would reduce production of 943 Type 4 fighters and the Navy would reduce production of 235 Ginga land-based bombers. From the perspective of materials, machine tools, and technical research, it was concluded that research on the Fugaku "regrettably must be discontinued." The Japanese military was defeated in the Battle of the Mariana Sea in late June 1943, and Saipan, which was the eastern key of the absolute national defense sphere, fell on July 6. Prime Minister Tojo, who had been the biggest supporter of the project, resigned on July 18 due to ostracism from those around him. Due to the policy of prioritizing the development of fighter aircraft for the homeland air defense battle and reducing the number of models developed, the development of the Fugaku was discontinued as it was deemed "not to be ready in time for this war."