Chapter II: Historical Record
(continued)

Japanese Naval Aircraft at Pearl Harbor

Nakajima B5N2 "Kate" Torpedo/Horizontal Bomber

Nakajima B5N (Kate)

In 1932 the Japanese began to develop a new series of carrier attack bombers capable of delivering torpedoes as well as bombs. Over a period of one year, the Japanese navy issued specifications needed to fulfill the needs of carrier warfare. Three companies in particular -- Aichi, Mitsubishi and Nakajima -- offered prototypes to meet the specifications. After careful evaluations were made, the navy again reissued the specifications in the hopes that it would be able to replace the B4Y1 Type 96 carrier attack bombers that had been accepted as a stopgap measure until suitable aircraft could be developed.

The new specifications called for a wingspan less than 52 feet 5 inches that could fold down even further and reduce the wingspan to 24 feet 7 inches. The airspeed must be in the area of 207 mph at 6,560 feet. For endurance it must be able to fly four hours at normal cruising and seven hours maximum. The crew must consist of three airmen. As for armament, it should be able to carry a bomb load of 1,764 pounds, either torpedo or equivalent bombs. To defend itself from aerial attack, a 7.7mm machine gun was to be mounted in the rear cockpit for crew operation. The general design was specific, as it called for a single engine monoplane.

In the competitive trials for a suitable design, the Nakajima team led by Katsuji Nakamura presented the Japanese navy with a configuration that went beyond expectations. The new aircraft, known as a Type K, was a sleek low-wing design with several options that made the craft ideal for future carrier operations. Among these innovations were: hydraulically operated undercarriage, folding wings, shortened fuselage (33 feet 9 inches) so that it could be used on existing carrier elevators in the fleet, and an airspeed of 230 miles per hour.

After months of flight testing, the aircraft (Type K) was redesignated (B5N1) Navy Type 97 carrier attack bomber model II. This aircraft flew from 1937 to 1939 where it saw limited action in the war with China. Because of the increased use of modern fighter aircraft being used by the Chinese, the Japanese saw a need to improve the aircraft to insure its survivability in combat. This led to the Navy Type 97 carrier attack bomber model 12 or B5N2. This aircraft had no external changes and was almost identical to the earlier B5N1. A dramatic change took place, however, internally. The main power plant had been the 9-cylinder Hikari 3 engine. In an effort to increase reliability, cowling-size reduction (increased visibility for pilot) and a small propeller spinner (reducing drag, that is, a cooler engine), the 14-cylinder double row Sakae II was adopted.

As the Japanese fleet trained in 1941, the B5N2 played a critical role in preparation for the Hawaii Operation. This aircraft had replaced all B5N1s and B4Y1s as the first line plane. At this point in history, Japan possessed the finest horizontal/torpedo bomber in the world.

Critical to the attack on Pearl Harbor was the successful execution of a torpedo attack on an anchored vessel. A great deal of training and technical engineering concerns had to be solved prior to the assault on Pearl Harbor. Fortunately for the Japanese, the training had gone well and the technical problems associated with shallow water torpedo attack were solved. However, one pilot, Lt. Jinichi Goto recalled:

We were told after reviewing what we have trained, we will start practicing against ships at anchor. They were anchored 500 meters from shore and we were supposed to attack from land. The depth of water was 12 meters. We were shocked to hear about it. To us it sounded senseless and we did not think we could do it ... In the beginning I was very nervous. I had stiff shoulders and my hands were shaking, but after a while I got used to it.

The fleet sailed for Hawaii in late November. Almost half of the attacking force was made up of B5N2s. A total of 143 planes, 40 torpedo bombers and 103 horizontal bombers were used that day. It was a spectacular success for the pilots and planes against the Pacific Fleet. For Lt. Goto, the attack on the battleship USS OKLAHOMA had left a lasting impression.

I was shocked to see the row of battleships in front of my eyes... I flew diagonally not knowing which was the bow and which was the stern. All I saw was the mast, the bridge and smokestack . . . three things were the key elements to the attack. Speed must be 160 knots per hour, the nose angle zero (meaning horizontal to the sea), an altitude 20 meters, We were told if one of these were off, it would change the angle and the torpedo would go deep under the water and miss the target... I didn't have time to say ready, so I just said fire. The scout man on the back pulled the release lever. The plane lightened, with sound of the torpedo being released. I kept on flying low and flew right through, just above the ship . . . I asked my observer "Is the torpedo going all right?" . . . Soon he said "It hit it" . . . Eventually, Murata's and my torpedo hit the mark. I saw two water columns go up and smoothly go down . . . But then I realized we're being attacked from behind . . . I was avoiding bullets by swinging my plane from right to left. I felt frightened for the time and thought my duty was finished. I headed back to the meeting place.

In just 15 minutes, the main battle line of the Pacific Fleet had been smashed. Large-scale operations of carrier warfare had come of age, and the old notion of battleship dominance slipped beneath the waters of Pearl Harbor.

As the war progressed, the decline of the B5N2 as a viable front-line weapon was evident. By 1944, staggering losses and in sufficient performance regulated the aircraft to second-line units. However, the Kate found a new avenue of effectiveness as a reconnaissance and antisubmarine aircraft. Because of its long flight time, the Kate was able to escort convoys and protect them from submarine attack. Radar and more sophisticated electronic gear were fitted to the plane to enhance the aircraft's effectiveness.

TECHNICAL DATA

Description: Single-engine three-seat carrier-borne torpedo bomber, all-metal construction with fabric-covered control surface.

Accommodation: Crew of three: pilot, observer/navigator/bomber-armer and radio-operator/gunner. Cockpit enclosed.

Powerplant: One Nakajima NK1B Sakae ii 14-cylinder air-cooler radial rated at 1,000 hp for takeoff, and 970 hp at 3,000m (9,845 ft.), driving a three-blade constant-speed metal propeller.

Armament: One flexible rear-firing 7.7mm Type 92 machine gun. Bomb-load: 8,900kg of bombs, or one 800kg (1,764 lb) torpedo.

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