AIR TECHNICAL INTELLIGENCE GROUP
ADVANCED ECHELON FEAF
APO 925

REPORT NO. 41
3 November 1945.

SUBJECT: Japanese Rocket Devices for Assisted Take-off for Aircraft (JATO).

REFERENCE: Hdqtrs. AAF, “Air Staff Intelligence Requirements in the Far East” dated 25 July 1945. Section III-A-1b.

PERSON INTERVIEWED: Lieutenant Commander Kumao HINO, I.J.N.

INTERVIEWING OFFICER: Commander N. B. KIERGAN, Jr., U.S. Navy.

BRIEF OF MATERIAL DISCUSSED:

1. Lieutenant Commander HINO served approximately ten years as a commissioned officer in the Japanese Navy, all in connection with naval ordnance. His major specialty was rocket propulsion, both projectiles and power devices, on which he did much of the research and design engineering.

2. Japanese fundamental research in rockets started in 1935. Their first tests on aircraft were made about 1940. The development of power units to assist aircraft started about 1943. Neither use of the rocket principle was developed to an extent approaching that attained in the United States.

3. The burning material developed for rockets, used in all applications, was chosen and designed for economy and ease of manufacture plus safety in handling and storage. Its composition, with purpose of each ingredient, was:

• Nitroglycerine – 27% – Energy source
• Mono-nitro naphthaline – 7% – Energy source
• Nitro cellulose – 60% – Energy source
• Centralite – 3% – Stabilizer
• Potassium sulfate – 3% – To give slow rate of burning; also as partial flame inhibitor.

The rocket grains made of this composition were always in the form of hollow cylinders, the size and dimensional proportions depending upon the configuration of the steel container and the desired amount and duration of thrust. A small amount of black powder was used as an ignition charge. All attempts to reduce smoke formation met with failure.

4. In the field of rocket projectiles, an attempt was made in 1940 to develop an armor-piercing rocket bomb to penetrate the armored decks of U.S. aircraft carriers. The attempt failed because the armor-penetrating feature required so thick an explosive jacket that only a small explosive charge could be used, and because of the excessively thick walls required on the rocket chamber to allow the high burning pressures required to give the unit a very high velocity.

5. An unusual land armament device utilizing rocket power was developed because a large supply of 250kg (550 lb.) aircraft bombs had been manufactured and there were insufficient aircraft to carry them. The device consisted of an inclined trough of wood or steel, about four meters (13 ft.) long inclined at 40°. A range of about 5000 meters (16,400 ft.) was achieved, but opportunity did not arise for large-scale use of this weapon.

6. As will be noted in Appendix (A), which furnishes tabulated data on all Japanese rocket devices, several types of land to air, air to land, and air to air weapons were designed, but relatively few saw appreciable actual application. This lack of use is considered attributable to (1) failure to achieve high performance and efficiency in the missiles, (2) lateness in starting development work, (3) necessity for using inferior propellants to permit easy manufacture, and (4) a pace of war which required new types of weapons faster than the Japanese could conceive. Some weapons shown in Appendix (A) might well have proven a serious threat if the military situation had ever made them applicable.

7. The same propellant was used in rocket power units for aircraft assisted take-off and similar uses, as stated above. A cylindrical propellant container with a venturi exit orifice was standard design. Suspension of the unit was by two lugs, one at each end; this required the use of a sway brace or clamping band. Firing or the ignition of the charge was by electricity, the pilot being provided with firing buttons for aircraft take-off work. Dimensions for one of the rocket units, obtained from a blueprint are:

Although the exhaust tube minimum I.D. does not agree exactly with data in Appendix (A), it is believed that the above dimensions apply to the 4.03 second unit (#17 on Appendix A). Attention is especially invited to the relatively long exhaust tube employed by the Japanese.

8. The primary use of Japanese rocket power units was as assisted take-off devices for aircraft. In this use, the pilot fired his rockets (JATO) at a point in the take-off run designated by a flag marker. This position was supposed to be such that the airplane would be airborne just before the rocket thrust stopped. Three sizes of rocket units were used, as noted in Appendix A. This system was used rather extensively for land-based aircraft, giving a take-off reduction of about 30 per cent, but never for patrol planes. Experiments were conducted with take-offs from aircraft carriers, but rocket smoke was considered to render the device impracticable for this use. Another experiment made with rocket units was to carry them attached to aircraft in flight, to give the pilot a short burst of extra speed when needed in combat. The idea proved completely unsuccessful because of the profile drag added by the rocket units.

9. The next use of rocket power was in the OKA-11 (BAKA). Three of the nine-second units were installed in the after fuselage, and the pilot fired them in succession when desired. They were intended merely to give the airplane additional range to permit a more accurate suicide dive. Each rocket unit was said to give a 1760 pound thrust for about nine seconds, indicating the probably use of No. 15 of Appendix A.

10. The final use of rocket units was as a power source for a land catapult. The catapult was intended to launch the OKA-43.
Design requirements were:

The catapult consisted of two rocket units mounted on a launching car (which carried the aircraft), which ran on a steel track. A hydraulic retarding system was provided to stop the car. The installation was completed at the TAKEYAMA Marine Base near YOKOSUKA in June 1945. Deadload tests proved successful, but aircraft launchings were not made before the Japanese surrender.

Prepared by: N. B. KIERGAN, Jr.,
Commander, U.S. Navy.

Approved: F. O. CARROLL,
Brigadier General, U.S. Army.