The use of near vertical incidence skywave (NVIS) propagation for HF radio communications somewhat beyond the groundwave range has assumed increasing importance in recent years, particularly when no artificial means of radio relay is available. When tracing its history however there has been a tendency to assume that it first made its appearance in military communications during the Vietnam war in the late 1960s. Certainly, in that conflict considerable use was made of NVIS techniques and the basic characteristics of the antenna systems intended to launch it were subjected to exhaustive measurement (1,2). However, the genesis of what is now almost universally referred to as NVIS (pr. envis) can be traced back at least to the Second World War when both the American and British forces used it - but never referred to it by that acronym.
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