The 1943 BRUSA Agreement was an agreement between the British and US governments to facilitate co-operation between the US War Department and the British Government Code and Cypher School (GCCS). It followed the Holden Agreement of October 1942.
Colonel Alfred McCormack of the Special Branch of Military Intelligence Service, Colonel Telford Taylor of Military Intelligence, and Lieutenant Colonel William Friedman came to Bletchley Park, the Government Code and Cypher School Headquarters in England in April 1943. The British decided to inform them of their successes with Ultra. The American trio worked with Commander Edward Travis (RN), the head of the British COMINT facility.
This led to the signing of the 1943 BRUSA Agreement on 17 May, which was a formal agreement to share intelligence information. It covered:
Even today the security regulations, procedures and protocols for co-operation form the basis for all SIGINT activities of both the US National Security Agency and the British GCHQ, see UK-USA Security Agreement.