Royal Navy Codebooks Carried Lead

Royal Navy signal codebooks were bound with thick lead panels so they would sink immediately if sailors threw them overboard to keep them from enemy hands. The Admiralty's S.P. 02201 signalling instructions, issued in 1935 and used throughout World War II, specifically included this safeguard. Crews had orders to destroy a compromised codebook by fire when possible, with throwing it overboard as the second-best option.

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