Nakajima G10N – strategic heavy bomber

Japan shared a fundamental flaw with Germany in regards to not developing a bomber capable of long range missions. The lack of this capability is considered by some to be a pivotal nail in the coffins of each country during the war. In both cases, efforts to develop such a bomber came too late to affect the outcome of the conflict. Although the Japanese had considered the need for such a bomber at the outset of hostilities – as had the Germans with the disastrous Heinkel He 177 Greif – very little happened until the need was dire, and by then the noose was tight, choking any hope for putting a long range bomber into service. The main cause of this apathy was the early success in the Pacific theatre where the short and medium range bombers then in use by the Japanese were adequate to fulfil the needs of the IJA and IJN. With the entry of the United When the tide of war turned against the Japanese, it was soon realised that some means to attack the US mainland had to be acquired, not only to destroy the war industry of America but to ravage the civilian population centres to reduce morale and bring the war to the US doorstep. In consequence, the US would have to allocate or divert resources to increase the defence of the homeland which would affect the war on other fronts. As history was to show, the Japanese did succeed in launching attacks against America, but only in the form of the Fu-Go balloon bombs and isolated attacks on the west coast from submarine-launched float planes. None had much of an effect.

There were some early attempts to produce a long-range bomber – for example, the Mitsubishi G7M1 Taizan (a 16-shi project) – plus designs that were actually built such as the Nakajima G5N Shinzan and Nakajima G8N Renzan. The Shinzan was not a success and the Renzan failed to reach operational States into the war a formidable problem arose. Geography put the military machine of the US far out of reach of Japan. service as a combat aircraft, let alone reach America and return.

It was to be Nakajima who would attempt to provide a strategic long-range bomber capable of bringing the war to America. The man behind the project was Chikuhei Nakajima, chairman and engineer of Nakajima Hikoki K. K. Motivated by his fears over the inability of the Japanese to reach and destroy US industrial capacity, Chikuhei tried to convince the IJN and the IJA of the need for a strategic bomber. However, officials from both services refused to consider his ideas. Thus, without official sanction or request, Chikuhei invested a portion of Nakajima’s resource to draft designs for a bomber that could take-off from Japanese bases, cross the Pacific, attack targets on the West Coast of America and return to either their original bases or elsewhere in Japanese or Axis held territory. Nakajima gave the design work the name ‘Project Z’.

On 29 January 1943, Nakajima began the task of assembling drafts and studies for the design of the bomber, along with reports which studied the feasibility and problems of production. On the completion of this stage in April 1943, he again pitched the concept to both the IJA and the IJN. This time, neither service turned Nakajima away. However, despite the information Nakajima had assembled for the proposed bomber, and despite both services now accepting the need for such an aircraft, the IJA and the IJN also produced their own ideas. Not surprisingly, the two services had differing opinions on the requirements for the bomber. The IJA desired a type that could operate at 9,998m (32,800ft) and carry a heavy defensive armament. By contrast, the IJN wanted a bomber capable of flying at a height of 14,996m (49,200ft), an altitude where interception would be minimal and thereby allowed a lighter defensive weapon load to be carried. Furthermore, the IJN wanted the bomber to take-off from Japan, bomb any target within the US, then utilise bases in Germany or German held territory to land, as opposed to making a round trip.

Though there were a number of variations of the aircraft during the Project Z development, three basic designs of what became the Fugaku emerged. The project presented by the IJA used a ‘tail sitter’ undercarriage, featured dual vertical stabilisers and bore some resemblance to German designs. It also had a rounded off nose similar to the Boeing B-29 Superfortress and Messerschmitt Me 264 ‘Amerika’ bomber. The IJN’s proposed design used a tricycle landing gear arrangement and rounded nose but utilised a single vertical stabiliser. Nakajima’s proposal kept the single vertical stabiliser but had a stepped nose much like that used on the G5N Shinzan which the company had previously worked on.

By June 1943, Nakajima had received plans from the IJA and IJN, reviewed them and begun work on drafting a final design. To continue the research and further development and study the Project Z aircraft, the Army and Navy Aviation Technical Committee was formed on 9 August 1943. The IJA delegation was headed by Captain Ando. Later in August, Chikuhei Nakajima prepared a thesis entitled ‘Strategy for Ultimate Victory’. Chikuhei used his personal clout to make sure his document reached not only IJA and IJN officials, but also politicians and even Prime Minister Hideki Tojo. His thesis was laid out in six chapters and contained Chikuhei’s plan for defeating the US as well as defending Japan. The key component was the Project Z bomber which he proposed could be used to destroy US airfields as a means to deny the US the ability to launch raids against Japan. This suggestion was in part due to his belief that Japanese air forces were not strong enough to repel a bombing raid. Another facet of the thesis was the use of the bomber to attack the US war industry. Without materials and oil, the US could not produce aircraft, tanks and other weapons. More importantly, he added, the Japanese should use the bomber to destroy the Soviet military industry as a means to support Germany. This implied that Nakajima could provide Germany with such long-range bombers.

The Project Z bomber would employ an all metal structure with the wings mounted in the mid-fuselage position. The plane was envisioned to be powered by the Nakajima Ha-54, 36-cylinder radial engine, also known as the D. BH. The Ha-54 was, in fact, two Ha-44 18-cylinderradials paired together. It was projected that the Ha-54 engine could produce up to 5,000hp and that six of these would be sufficient to propel the bomber to a generous maximum speed of 679km/h (422mph). Each engine would drive two contra-rotating, three-bladed propellers with a 4.5m (14.7ft) diameter. The Ha-54 engine, however, would not be ready for some time (and as events turned out, by war’s end it was still only a prototype engine and problems with cooling the power unit through the use of a ducted cowling were never solved). Therefore, Nakajima had to settle for the experimental NK11A (Ha-53) which, while also in development, was expected to be ready for trials. The drawback was that the NK11A was expected to muster only 2,500hp and this would certainly have lowered the performance estimates. The introduction of the NK11A meant that a revision of the Project Z airframe became necessary.

The bomber’s ceiling was estimated to be 15,000m (49,212ft) and it was believed that a heavy defensive armament was not necessary as the high altitude would offer protection from fighter opposition. To a lesser extent the projected speed would also reduce vulnerability. Consequently, the bomber would carry at least four Type 99 20mm cannons, but contemporary illustrations of the bomber often show a much heavier armament. This may be a result of having to settle for the less powerful NKIIA and any speed/altitude advantage would have been lost, so an increased weapon load would have been necessary to protect the aircraft. Typically, illustrations show two cannon mounted in the tail, two in the nose, two twin-cannon turrets placed in the front and rear of the fuselage top and at least one belly turret. Variations included waist gunner stations. For a normal bomb load, the bomber was expected to carry up to 20,000kg (44,092Ib) of bombs, but in the case of anti-shipping missions, torpedoes could be carried (see below). For attacks on the United States, the bomber would carry only up to 5,000kg (11,023Ib) of bombs.

As work continued on the Project Z, plans were made to assemble and house the bomber’s production line. By the fall of 1943, these plans had been completed and construction of the new facility had begun. By January 1944, the Project Z moniker was dropped and changed to the Fugaku which means ‘Mount Fuji’.

As it was, more pressing demands on Nakajima resulted in less and less work being done on the Fugaku. To compound the problem, by the time the design was nearing completion, Japan was on the defensive and chances of producing the Fugaku, let alone using it to attack America, were about nil. The UA believed that there was no probability of the Fugaku being built and therefore abandoned the project, leaving the UN as the sole remaining party involved. Even the Gunjusho (the Ministry of Munitions) felt the Fugaku was impossible to realise and ordered Kawanishi to design a new long-range bomber. Unfortunately, the Gunjushō failed to inform the UA, UN and Nakajima about the Kawanishi bomber, which was known as the TB. When the new bomber project was discovered, a hail of protests and arguments erupted that hampered not only the development of the Fugaku but all long-range bomber projects including the TB which was soon cancelled.

However, it was the fall of Saipan in 1944 that sealed the Fugaku’s fate. The Japanese air forces no longer had need of a super long-range bomber and demanded more pertinent aircraft to protect the mainland. As such, all work on the Fugaku was stopped and the plans, calculations and drafts were shelved. Work on the production facility was halted prior to completion and left unfinished. With the Japanese surrender, all documentation for the Fugaku was to be destroyed to prevent the information being handed over to the Allies. Papers on the Fugaku that survive to this day, including a number of drafts for various Project Z/Fugaku proposals, were mislaid or kept for safe-keeping by individuals. Since the war it has been claimed that the Misawa Air Base would have been used by Fugaku bombers to launch raids against the US. While Misawa was used by the UA and operational UA bombers flew from this facility, there has been no definitive evidence to support or refute Misawa being considered as a Fugaku base.

Bombing was not the only mission that was envisioned for the Fugaku and during the Project Z brainstorming three other concepts arose and later formed part of Chikuhei’s thesis. The first was an attack design that had 400 Type 97 7.7mm machine guns crammed into the aircraft. The front and the back of the bomber would accommodate 40 machine guns arranged in ten rows. The intention was to rain thousands of rounds of bullets down on to enemy ships with the theory that a swath of destruction 45m (148ft) wide and 10km (6.2 miles) long could be achieved by 15 Fugaku aircraft. Once the decks of these ships were swept of personnel, nine Fugaku bombers, each with twenty 907kg (2,000Ib) bombs or torpedoes, would deliver the coup de grace, covering a path 200m (656ft) wide and I km (0.62 miles) in length with high explosive.

Another version had the Fugaku loaded with 96 Type 99 20mm cannons. The front and the back of the aircraft would contain 12 cannons arranged in eight rows while another 36 cannons were fitted on each side of the aircraft. This particular variant was to target enemy bombers flying missions against Japan and would use hidden bases untouched by the Japanese airfield bombing campaign. By flying over the enemy bomber formation and unleashing a withering fusillade of cannon fire, it was speculated that ten of the cannon equipped Fugaku could bring down 100 bombers, the area covered by the cannons from one plane being 2.5m (8.2ft) and 3km (1.86 miles) long. A system of ground radar stations would give advance warning of the incoming enemy bomber force, allowing time for the Fugaku to intercept and destroy the bombers before they reached Japan. This was all very impressive on paper but had it been put into practice the results were likely to have been less than stellar, especially when considering the failure of the Mitsubishi G6M1 heavy escort fighter (a G4M converted into a gunship to provide cover for bomber formations). Finally, the Fugaku was considered as a transport which would have provided a significant heavy lift capability. It was estimated that one Fugaku transport would be able to carry 300 soldiers with full equipment, about equal to one infantry rifle company with a heavy weapon platoon. Chikuhei envisioned a grand scheme of a raid against America where four hundred transports would deposit 120,000 men (equivalent to a Japanese Army, which equates to a US and British Corps) on US soil to take over the Seattle-Tacoma airport located in Washington. After landing the troops would move overland to attack and destroy Boeing’s B-29 producing Renton Factory in Renton before returning to Japan.

There is no evidence to suggest any of these concepts made it to the final Fugaku designs. However, if any of the three ideas were supported, a transport may have topped the list for possible consideration given the late war need for aircraft capable of bringing raw materials into Japan to feed the war industry that was slowly being starved. As a note, although the designations G10N and G10N1have been used in print for this aircraft for many years, there has been no confirmation in historical sources that confirms this was the case.

Specifications (Project Z / Fugaku projected)

General characteristics

Crew: 6 to 10

Fugaku: 7 to 8

Length: 44.98 m (147 ft 7 in)

Fugaku: 39.98 m (131 ft)

Wingspan: 64.98 m (213 ft 2 in)

Fugaku: 62.97 m (207 ft)

Height: 8.77 m (28 ft 9 in)

Wing area: 352.01 m2 (3,789.0 sq ft)

Fugaku: 330 m2 (3,552.09 sq ft)

Aspect ratio: 12.1

Empty weight: 65,000 kg (143,300 lb)

Fugaku: 33,800 kg (74,516.24 lb)

Gross weight: 122,000 kg (268,964 lb)

Fugaku: 42,000 kg (92,594.15 lb)

Max takeoff weight: 160,000 kg (352,740 lb)

Fugaku: 70,000 kg (154,323.58 lb)

Powerplant: 6 × Nakajima Ha-54 36-cyl. air-cooled radial piston engines, 3,700 kW (5,000 hp) each at take-off

Fugaku: 6x Nakajima NK11A 18-cyl. air-cooled radial piston engines developing 2,500 hp (1,864 kW) at take-off

Propellers: 6-bladed contra-rotating constant speed propellers, 4.5 m (14 ft 9 in) diameter

Fugaku: 4-bladed constant speed propellers 4.8 m (16 ft) diameter

Performance

Maximum speed: 679 km/h (422 mph; 367 kn) at 10,000 m (32,808 ft)

Fugaku: 779 km (484 mi)at 10,000 m (32,808 ft)

Range: 17,999 km (11,184 mi; 9,719 nmi) maximum

Fugaku: 19,400 km (12,055 mi)

Service ceiling: 15,000 m (49,213 ft)

Wing loading: 456.99 kg/m2 (93.60 lb/sq ft)

Fugaku: 211.89 m² (43.4 lb/ft²)

Power/mass: 0.103 kW/kg (0.063 hp/lb)

Fugaku: 0.118 kW/kg (0.07 hp/lb)

Armament

Guns: 4× 20mm Type 99 cannon

Bombs: 20,000 kg (44,092 lb) of bombs

It’s very difficult to find precise Fugaku variant drawings.

Almost all drawings were lost.

Base design: Nakajima  HA54 engine (5,000hp in take-off) ×6

Variant 1: Nakajima  HA44 engine (2,500hp in take-off) ×6

Variant 2: Mitsubishi HA50 engine (3,000hp in take-off) ×6

Variant 3: Kawanishi design

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