19. AIR-GROUND

Through air reconnaissance coupled with close radio communication with the advanced elements of the ground forces has enabled the Japanese frequently to out-maneuver their opponents. This was possible because of their air superiority. Company commanders of ground forces carry portable radios with attached earphones. The radios are strapped to their chests like gas masks in the alert position. Supporting aircraft notify the companies when they should advance or halt. The company commander, in turn, waves a flag to planes when he moves forward and when he orders a halt. Such portable sets also are used to maintain continuous liaison with adjacent companies, for communications during beach landings, and for communications from points in rear of United Nations' lines to Japanese headquarters. They have an effective range up to 35 miles. All of Japan's new planes are equipped with modern two-way radios.

20. GROUND

Signal communications from the division downward follow the general orthodox system of using radio, motorcycle, and bicycle messengers and occasionally visual signaling. Extreme simplicity characterizes the operation of the system-short mission orders, direct oral orders, and flag signals. The regimental radio communication system usually extends down to company headquarters. Each company commander has a pool of runners for communication down to the platoon. Within the platoon a noncommissioned communications officer maintains contact between squads and the platoon, either orally or by use of runners.

All Japanese commanders' tanks down to the platoon are equipped with two-way radios.

Small armored motor launches are used to maintain intercommunications during landing operations.

21. EQUIPMENT

Signal equipment conforms generally to that indicated in TM 30-480, Handbook on Japanese Military Forces. Radio equipment is well made and bears dates showing storage since 1935. All radio sets are operated by dry battery and are ruggedly constructed. An aircraft set functioned well after having been dropped more than 2,000 feet with no repair except the replacement of its vacuum tubes. One captured 60-pound portable, all-wave receiver operated very satisfactorily.

22. RADIO JAMMING

Units for jamming are included in each signal regiment. Most jamming to date is reported to be on broadcast frequencies. However, jamming of tactical frequencies in the range from 5 to 8 megacycles and of point-to-point frequencies as high as 15 megacycles has also been reported. Jamming on point-to- point circuits was readily overcome by continuing traffic on the jammed frequency, as well as on another frequency. Methods of jamming used are the following:

a. Transmission of dummy messages and call signs from a tape recording on a frequency corresponding to that to be jammed;

b. Transmission of a carrier wave of frequency corresponding to the frequency to be jammed and modulated by raw alternating current;

c. The use of a howler or fluctuating continuous wave carrier to interfere with radiotelephone transmissions.

In general, it may be said that the Japanese jamming efforts were unskilled and ineffectual.

23. CODES AND CIPHERS

In general, Japanese codes are of the book type with one-time deciphering tables. Transmissions by radio of bearings from ground stations to aircraft on bombing missions are generally in the clear. Sometimes the Japanese use a simple three-letter code, which is readily broken. This code is used for economy, not for security.

24. RADIO INTELLIGENCE

The efficiency and accuracy of intercept units is indicated by Japanese attempts to masquerade radio stations as those of their opponents, in which attempts they used procedure signs derived from intercepted messages.