There is within the PRO archives Churchill’s message to Roosevelt on the 16^th January  giving a suggested joint reply to Stalin's request for a share of the Italian Fleet and a discussion on what communications channels to be used using Magic, so it was a regular thing for information to be passed from the UK to the USA using Ultra and Magic.

Throughout the war Purple and Magic like Enigma and Ultra, were to provide the Allies with intelligence that no doubt helped to forestall and eventually defeat the Axis powers. It provided in the European theatre information on how Rommel built up his forces in North Africa, and in the Pacific intelligence that supplemented the USA’s Naval forces knowledge.

However there was a down side to this, and that was  how to keep secret from your enemies the fact that you can read their intelligence.  For Brittan it was no problem, we had the "D" note, a mechanism that prevented news papers from reporting anything that may harm its existence.

But in America the press had a free reign and could publish at will, and they did, to the extent that knowledge that the US Military knew of the Japanese strength was reported in the press after the battle of Midway.

INDEX

A disaster that had consequences, for the Japanese changed their codes and were alerted to the fact that its Purple codes had been broken.

But it must be realised no matter what we knew about the proposed moves by the Japanese or the German military strategy through intelligence gathering, it could only be used with the troops we had on the ground.

PRO record HW 50/13/2. B Machine (Japanese Diplomatic) Anglo/US Cooperation. Notes on the US release to Britain of their greatest secret, the Japanese high-grade diplomatic cipher machine Purple pencil notes by Frank Birch 1^st February 1942  – 2^nd May 1945.

GCHQ Government Code and Cipher School and Government Communications Headquarters: Records relating to the writing of the history of British signals intelligence in World War II

HW 1/2344 Signals intelligence passed to the Prime Minister, messages and correspondence. Detailed descriptions at item level

The following are a few of the Decrypts of German intelligence made by Ultra, code word BONIFACE by Government Communications Headquarters (GCHQ) in the PRO HW series.