Signal operating instructions

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Signal operating instructions (SOI) or Communications-Electronics Operation Instructions (CEOI) are U.S. military terms for a type of combat order issued for the technical control and coordination of communications within a command. They include current and up-to-date information covering radio call signs and frequencies, a telephone directory, code-words (for rudimentary encryption), and visual and sound signals. A designated <a href="/facts/Battalion/AohlXDhb">battalion</a> signal officer prepares the battalion SOI in conformance with the SOI of higher headquarters. During operations, SOI are changed daily. Since the fielding of the <a href="/facts/SINCGARS/qXoJcGVM">SINCGARS</a> system, however, the paper SOI has generally faded from Army use. Electronic SOI are now generated, distributed and loaded along with <a href="/facts/Key_(cryptography)/5W5PAmT4">cryptographic keys</a>.
</p><p>The title SOI was used until the early 1970s and it was changed to CEOI and then changed back to SOI in the 1980s.
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Signal operating instructions open-in-new

Signal operating instructions