For more than 30 years, the Vietnamese revolutionary movement successively fought Japan, France, South Vietnam, and the United States of America in its successful struggle to establish an independent and socialist Vietnam. Although many aspects of these wars have been described and analyzed by both the winners and losers, one significant topic has been almost entirely absent from the discussion - the Vietnamese development and use of cryptography to maintain their movement's communications security. "Essential Matters: A History of the Cryptographic Branch of the People's Army of Viet-Nam, 1945 - 1975," a translation of a 1990 Vietnamese government publication, tells the story of how Vietnamese cryptographers, through trial and error, developed an indigenous cryptography, supplemented by China-trained experts who introduced more sophisticated techniques to enhance their colleagues' efforts. Many of the these revolutionaries were more conversant with French because of that language's dominance in the colonial education system, so they were forced to subject their own language to the most basic analysis of structure, its specialized military and technical vocabulary, the frequencies of its letters and words, and its subsequent rendering for cryptographic and radio transmission purposes, all encouraged at the local level by the revolutionary leadership. The result was the employment of a multiplicity of similar cipher systems, which presented a major challenge to the movement's various military adversaries. "Essential Matters" records the names of the individuals who performed this arduous work under difficult conditions, describes their training, and portrays their hardships and suffering - approximately 500 Vietnamese cryptographers, nearly 10 percent of those on duty as of 1972, were killed in the course of their duties. This remarkable account, which includes a supplement drawn from "A History of the Cryptographic Branch of the Border Guard" that extends the coverage of Essential Matters by 14 years, into the cipher machine era, provides a unique portrait of a little-known part of the Vietnamese military and its contribution both to cryptography and the outcome of the Indochina wars.