The Battle of the Atlantic: Allied Naval Intelligence in World War II


M4 Enigma
Courtesy of the National Security Agency Cryptologic Museum
The Mariners' Museum photograph by Gregg Vicik

Highly complex, "Enigma" machines were used aboard U-boats to cloak messages transmitted by radio. Most German naval leaders believed their code and cipher systems unbreakable. However, key components fell into Allied hands, enabling the Allies to solve Enigma with relative consistency. After 1943, U.S. Navy forces used the information derived from intercepted radio transmissions and Enigma to hunt down U-boats.