US Army Military Intelligence History: A Sourcebook - Fort Huachuca ...

U.S. Army Intelligence History: A Sourcebooktions equipment and provided intercept operators with a valuable guide to the operational range andcharacteristics of Viet Cong communications. 15The Communist DefensesThe enemy’s security did not crack easily. A wary people by nature, the North Vietnamese hadcloaked the insurgency in South Vietnam in a pervasive secrecy. Captured communications securitydirectives indicated that as early as 1962 the Communists were taking a serious and sophisticated approachto protecting their communications. For example, they permitted unencrypted transmissions only onnews broadcasts. 16Besides the Communists’ natural predilection for secrecy, an unswerving adherence to directives andplans within the ranks enhanced the security of Communist communications. Communist radio operatorswere more likely to follow rigid security directives than their more highly educated American contemporaries,who tended to interpret rather than follow directions and to look for shortcuts which sometimescompromised communications security. Because the Communists maintained tight discipline over theirtroops, they also could plan and rehearse operations in precise detail with the confidence that each stepwould be carried out exactly as directed, a factor that lessened the need for communications for commandand control during those operations. Less communications, in turn, meant fewer opportunities for Americansor South Vietnamese to use electronic warfare against Communist communications.In addition to strictly regulating communicators, the Communists educated other staff officers to maintaincommunications security. They enjoined them to avoid using electrical transmission whenever courierservice was available. Any information transmitted by radio had to be protected even after it was nolonger classified, lest an enemy discover it in an unencrypted form and break signal codes by comparingthe text of encrypted and unencrypted communications. Perhaps the greatest impetus to enemy communicationssecurity was the universal belief throughout the ranks that the Army Security Agency was practicingelectronic warfare against Communist communications. 17The Central Office for South Vietnam distributed codes, call signs, and frequency assignments to thesignal staffs at each military region headquarters, where signal representatives from units and provincespicked up extracts of the information pertaining to their own operations. From those extracts each radiooperator copied into a notebook only that information that applied to him. Although much less efficientthan the American practice of mimeographing an entire package of communications information, calledSignal Operating Instructions, and giving it wide distribution, the enemy methods were far safer. Bystrictly controlling distribution, signal officers not only limited the amount of signal information vulnerableto capture but also made it impossible for radio operators to enter any nets in which they did notbelong, a practice that could cause breakdowns in net discipline and security.The Viet Cong assigned professional cryptographers to every regiment and every province. Sinceradio operators were kept physically separated from the cryptographers and were even forbidden to associatewith them during off-duty time, radio operators had little opportunity to handle or have knowledgeof any annunciated classified information. Besides restricting access to important cryptographic material,the compartmentalization of communicators and cryptographers precluded the inadvertent transmission ofclassified information in the clear by a careless radio operator. Because of the sensitive nature of cryptographers’work, they were usually handpicked Communist Party members who had received intensivetraining at a special school in Hanoi. 18Even in low-level units without cryptographers, radio operators followed precise operational proceduresthat made communications more secure. The Communist practice of communicating with eachstation on a net only at a scheduled time and on a prescribed frequency—and of varying those times andfrequencies periodically—made it difficult for an enemy to intercept a particular station by continuallymonitoring a signal frequency. The enemy made mandatory the use of international procedural words,called prosigns, to communicate signal information. Using these shortcuts meant that transmitters were252