Memorandum, Notes on Use of Code

DECLASSIFIED E.O. 12065, Sec. 3-402 Seerer DOD Directive 5100.30, June 18, 1979 E By NLT- NC NARS, NOTES ON USE OF CODE Date 5-20-12 TO BE ISSUED DOWN TO COMPANIES. TO BE COMPLETELY DESTROYED AFTER BEING READ. In order that information and reports, when they must be transmitted by radio-telegraphy or other means subject to interception, may not furnish valuable information to the enemy, some form of code or cipher is necessary. No cipher sufficiently simple to be used in the field will long resist solution. For this reason, their use should be limited to absolute necessity, and messages made as short as possible. The "Playfair" cipher has been in use for many years, and is regarded as the best means for temporarily concealing the meaning of a message when a code book is not available. It can, however, be solved in a few hours, and should never be used except in emergency. The safest means of preparing messages for transmission is by use of a code book. The code book now issued to divisions will, if properly used, be entirely safe for a period of from two to four weeks. If instruc- tions are disregarded, and groups unnecessarily repeated, or "nulls" omitted, or if the code book is used for routine "form" report, the enemy will probably be reading your messages within a week. The surest ways of helping the enemy in the solution of your code are to send a large number of spelled-out words (one group for each letter), or to send part of the message in clear and part in code. A very few messages of this kind will give enough solutions to enable most other messages to be read. The instructions printed in the code book are based on actual solution of enemy codes, and their impor- tance cannot be overestimated. To show the serious consequences of disregarding instructions contained in the code book and in General Orders No. 103, G. H. Q., 1918, the following instances of carelessness, or worse, are quoted: (1) A division engaged in maneuvers in the rear area sent messages reporting progress of various units during the maneuver. These messages gave organizations and names of commanders in clear. This division might as well have notified the Germans definitely of its location, of the organizations forming part of the division, and of its future intentions. (2) In one organization six code books were lost in action and that fact reported only after the return of the code books had been demanded. Whether these books reached the hands of the enemy or not is not known. No harm was done, for the reason that officers, with a greater sense of responsibility, lost books at the same time and made immediate telegraphic report of that fact, thus insuring the issue of a new edition of the code. (3) Code messages with address in clear have been intercepted by our control station, and if intercepted by the German stations, gave the exact location of various units. (4) A number of messages in straight code contain no "nulls." Such messages are always desired by enemy code men. (5) Many messages contain unnecessary repetition of code groups. In one instance, a message of less than 30 code groups contained the letter "E" repeated three times. The first code group appearing after "E" was used each time. From that one message, the Germans were able to make a good guess at to which one of our code groups stood for "E." (6) One officer reports the destruction of all the code books in his organization because the division was moving forward and he had no safe in which to store his books. While the destruction of code books to pre- vent capture is entirely proper, this officer destroyed his books at the very time they might be of the greatest use to him. (7) Orders now permit the destruction of code books when a new issue is made. The greatest care, how- ever, must be taken that the books are actually destroyed. There are now on file in this office certificates to the effect that certain code books have been destroyed in the presence of the officer signing the certificates. The code books themselves are also on file here. If this can occur with respect to code books returned, it would seem that it could also occur with respect to code books captured by the enemy. The greatest care in verify- ing the destruction of code books is essential. To meet the demand of companies and other organizations for a very short code which will permit the sending of important messages without the delay now required to search through a rather large book, there is being published an emergency code list. This will contain about 50 of the phrases most used at the front. It will be republished and issued with each edition of the code book. Its return after use will not be required. It will be printed on a single sheet, which can be readily destroyed, and no effort should be spared to keep it out of the hands of the enemy. It should be clearly understood that any carelessness in the use of our code endangers not only the officer or organization concerned, but every Allied organization on the Western front. Before the March offensive the Germans published a complete new code for use by all troops on the West- ern front. This code was entirely different from anything that had yet been used, and its appearance was re- garded as an indication of a coming offensive. Its solution was considered one of the most important duties /orward to to quintly