The British codebreakers needed to know the wiring of the special naval Enigma rotors, and the destruction of by in February 1940 provided this information. In early 1941, the Royal Navy made a concerted effort to assist the codebreakers, and on May 9 crew members of the destroyer boarded and recovered her cryptologic material, including bigram tables and current Enigma keys. The captured material allowed all U-boat traffic to be read for several weeks, until the keys ran out; the familiarity codebreakers gained with the usual content of messages helped in breaking new keys.