The codebook goes over the side
On January 23, 1968, North Korean gunboats closed on the USS Pueblo, a lightly armed American spy ship off Wonsan. The crew had minutes. They swung fire axes at code machines and fed documents into a small incinerator that could not keep pace. Mattresses caught fire below decks. One sailor died in the shelling. When the boarding party came over the rail, most of the classified material aboard was still intact. The NSA damage assessment, declassified decades later, estimated that 50 to 80 percent of the documents aboard fell into North Korean hands. It described the destruction effort as disorganized and carried out in near total confusion.
The Navy had planned for exactly this moment. Codebooks of that era were bound in weighted covers so a radio operator could throw them over the side and watch them sink. Emergency destruction was a written bill, drilled like firefighting. The Pueblo failed the drill, and NSA historians counted the loss among the worst in the history of American cryptology. The failure was operational. The doctrine itself was sound. Some knowledge must die rather than be taken.
Eleven years later the lesson repeated in Tehran. The American embassy had replaced its slow furnaces with paper shredders. When students stormed the compound in November 1979, staff shredded what they could not burn. The students then enlisted local carpet weavers to reassemble the strips by hand, knot by knot, page by page. The reconstructed files were published as Documents From the U.S. Espionage Den, a series that ran to dozens of volumes and burned sources for years afterward.
Militaries have understood this duty for as long as they have written things down. The burn barrel sat next to the safe. The demolition charge sat next to the crypto gear. The duty to destroy was as real as the duty to collect, and every operator knew which one came first when the perimeter broke. Then software arrived, and the duty quietly disappeared.