[mjbollinger]

Thanks, Bruce.

Not sure I agree with your view that UK-US SIGINT cooperation predated Churchill. The transfer of SIGINT methods almost certainly began with the meeting on 8 Jul 1940 between Lord Lothian and FDR. While we don't know what was discussed on this specific topic in this meeting, we now know (as of recent 2010 NSA document releases) that FDR, Stimson and Knox approved the sharing of cryptological methods on 11 July 1940 and that Donovan took off for London three days later. This is prior to the Standardization of Arms Commitee meetings which I believe (without proof yet) were in part cover for the cryptological cooperation.

I've never encountered any data that suggest there was cryptological cooperation prior to that point. If you have some, I'm keen to learn more.

As for OP-20-G, they dragged their feet compared to the US Army. On 5 September 1940 Gen. Strong asked Gen. Marshall to include Army cryptological methods in the technical exchanges under the Standardization of Army Committee. Marshall agreed but could not get the Navy to participate. There are indications that OP-20-G was permitted to request SIGINT information from GC&CS beginning in late September but it is unclear when the first transfers took place. There are rumors of submarine tracking charts in OP-20-G that have annotations linked to ULTRA and I intend to pursue that line of research.

My sneaky suspicion is that the UK agreed to share submarine SIGINT-based information with the US (without indicated whether it came from basic Y-Service tracking or decrypted messages) in return for the US policies to openly broadcast the positions of any submarines sighted in the Atlantic. This would have provided cover in 1941 for any sudden success of Royal Navy escorts in tracking and destroying submarines, diverting suspicion from the fact that the Brits had broken the Enigma / Dolphin code.

Marty