COMMUNICATIONS IN AIRCRAFT CONTROL
C. VERY HIGH AND ULTRA HIGH FREQUENCY RADIO--VHF AND UHF.
D. HIGH FREQUENCY RADIO--HF.
E. ASSIGNMENT OF FREQUENCIES.
H. RADIO DISCIPLINE.
COMMUNICATIONS IN AIRCRAFT CONTROL
Radio is the primary means of modern aircraft communications. Continuous-wave transmissions, electronic, and visual signals are used to a limited extent, but the great majority of all messages are transmitted by radio telephone circuits. This provides an accurate and extremely rapid means of direct communications over great distances.
In using radio careful consideration must be given to the problem of security. The enemy can receive our transmissions and may gain knowledge therefrom which can be of great help to him. In addition to intercepting messages, the enemy may discover, by use of direction-finding devices, the position of the transmitter and thus the position of our units. Various
security measures are taken to minimize these dangers.
C. VERY HIGH AND ULTRA HIGH FREQUENCY RADIO--VHF AND UHF
Choosing the proper frequency depends primarily on the mission involved. Transmissions on frequencies of approximately 30 megacycles and above possess a characteristic not found in the lower bands. They are quasi-optical or line-of-sight transmissions. In other words these transmissions will not, except under freak conditions, follow the earth's curvature. VHF/ UHF is therefore well adapted for intra-task group communications since, regardless of the power used, ships or stations below the horizon cannot normally intercept the transmissions. This condition must not permit the development of a false sense of security among users of VHF/UHF.
In working with aircraft VHF/UHF affords reliable communications out to about 100 miles and often considerably farther providing the plane has sufficient altitude to put it above the horizon. VHF/UHF is now used exclusively by all aircraft for all missions within effective range of this equipment.
D. HIGH FREQUENCY RADIO--HF
For long-range transmissions when planes are below the horizon it is necessary either to use lower frequencies or to station VHF/UHF relays every hundred miles or so. In employing HF the use of the minimum necessary power is a good security measure. Also there are bands in the lower frequencies which possess certain peculiarities such as skip distances and difficulty in D/Fing. These peculiarities are taken into consideration by communications officers when drawing up frequency plans.
The use of HF in aircraft control is much less extensive than that of VHF/UHF. HF is used principally by planes when over an enemy target or when they are well away from our units. Generally, the high frequencies used are common throughout a task force. On rare occasions it will be possible to establish HF/CW communications when voice communications fail. CW has greater range than modulated transmissions but it is much slower.
E. ASSIGNMENT OF FREQUENCIES
In assigning radio channels for any air opera- tion first consideration is given to the frequencies available and the type of equipment employed. Having this information at hand, the channels are assigned in such a way as to permit the widest possible dissemination of in-formatiton while yet avoiding congestion arising from excessive traffic on individual channels.
Assignment of frequencies for various nets listed in USF 15 and USF 70 (B) is done by USF 70 (B) and the communication plan for each individual operation.
Aircraft radio telephone communications are generally sent in plain language. High security codes are not well adapted to the requirements of speed and simplicity which characterize aircraft communications. Simple, frequently changed codes are necessary, however, for concealing information involving times, bearings and distances, courses and speeds, and the like, especially when they deal with operations sufficiently far in the future to permit the enemy to take effective countermeasures.
A typical example of this is the "shackle" code which substitutes letters for numbers and changes daily or in accordance with existing instructions. The shackle code is not difficult to break down, but the delay attendant in breaking it down is such that it serves the purpose for which it is intended. Unless proper procedure is used in each case, however, compromise of the daily shackle list is apt to occur.
Decipher Examples A-5 N-1 1. "Will attack at shackle Victor Oboe Charlie Sugar." B-7 O-2 C-0 P-9 D-8 Q-6 Meaning: Will attack at 1200. E-5 R-4 F-5 S-0 2. "ETA shackle Charlie Peter Yoke Zebra group composed of shackle Nan Charlie unshackle Victor Foxes shackle Charlie Able unshackle Victor Able." G-2 T-9 H-8 U-3 1-7 V-l J-5 W-6 K-l X-3 L-4 Y-0
Decipher Examples M-0 Z-0 Meaning: Estimated time of arrival 0900.
Group composed of 10 VF, 5VB, 5VT.
The "Joint Air Warning and Air Defense Code" (JANAP 142 series) is not a true code, for it offers only a slight degree of security. It was designed to expedite communications rather than to serve as a security system.
Besides intercepting our transmissions, the enemy sometimes attempts to counterfeit transmissions and gives false orders or information to our forces. A system of authenticators is used to counter this move. An addressee who is suspicious of the source of a message should demand proper authentication before taking any action. To challenge, transmit "Say again and authenticate," or "Authenticate your last transmission." In order to prevent enemy use of the authenticators they are changed daily, and CIC personnel must be cognizant of them.
H. RADIO DISCIPLINE
Strict radio discipline on aircraft circuits is essential to efficient operations. Since upwards of 100 planes may be on the same channel simultaneously, unnecessary transmissions must be completely eliminated. A thorough understanding by the pilots of rendezvous procedure, lost plane procedure, K/T procedure and the use of visual methods of communication is of great importance in this connection.
I. RADIO SILENCE AND RADAR SILENCE
To assist in setting up a communications plan, various conditions of radio and radar silences are defined in fleet publications. These conditions limit the use of the different frequency bands. While en route to an objective, strict limitations may be placed on the use of radio and radars, but once the attack has commenced and our presence is known to the enemy, discipline may be relaxed. The OTC prescribes the effective conditions of radio and radar silences to conform with the tactical situation. (See USF 15 and USF 70 (B).)
Table of Contents
Previous Chapter (3) Next Chapter (5)