During WWII, some US military documents contained a notice stating, "This telegram must be closely paraphrased before being communicated to anyone." This raised the question of why paraphrasing—rewording a message without changing its meaning—was required rather than sharing the exact text. The phrase suggests careful rephrasing to prevent leaking plaintext information that could aid enemy cryptanalysis. An accepted answer on History Stack Exchange references a 1950 US Army Technical Manual (TM 32-220, "Basic Cryptography") that discusses this practice. The manual advises never to send identical plain text more than once in cryptographic or clear form, as doing so compromises security. When information must be distributed widely or publicly, the plain text should be carefully paraphrased—rewritten substantially by changing sentence order, using synonyms, and eliminating repeated words—to minimize the risk that an enemy could match plaintext with encrypted messages and break the cipher. This practice was critically important because enemy cryptanalysts could exploit repetitions of the same message transmitted with different encryptions to decipher stronger ciphers, as was famously the case with the German Enigma machine. Paraphrasing thus served to protect cryptographic security by preventing exact matches between plaintext and encrypted messages. The term "must be closely paraphrased" means that rewording should be done very carefully to preserve meaning but avoid identical wording. Comments in the discussion highlight the dual meaning of "closely": it implies both keeping the meaning very close to the original and exercising great care in rephrasing. The essence was to ensure accuracy while altering the wording enough to prevent cryptanalysis by comparing multiple versions of the same message. In summary, the phrase was a security protocol instruction to carefully reword sensitive telegrams before wider distribution, to avoid providing attackers with matching plaintext and ciphertext pairs that could be used to break encryption systems.