The Finnish signals intelligence service of WWII was able to solve many foreign cryptosystems including Soviet military and NKVD codes and the diplomatic systems of the United States. Many of these messages can be found in the Finnish national archives. The decoded diplomatic traffic can be found in folders T-21810/4 and T-21810/5.
It is interesting to note that a lot of the traffic from Bern, Switzerland consists of reports on the German military and the war industry. These were probably prepared by the OSS Bern Station and the US military attaché Barnwell R. Legge.
Here are some of these messages:
Folder T-21810/4 – messages of 1943
The Vatican requests information on POW officers in Crossville, Tennessee
Reports by US ambassador Laurence Steinhardt on negotiations between SU foreign minister Molotov and Turkish government
Office of Strategic Services requests that US embassy in Turkey pay 10.000 dollars to Albanian minister Dshadshuli
US report from Bern regarding shipping of raw materials essential to the German war effort
Report by General Barnwell R. Legge, US military attaché in Bern, on German manpower reserves
Turkish report on the troops of the Soviet Ukrainian Front
Turkish account of Molotov speeches regarding peace negotiations with Finland
US report from Bern on French resistance
Report on French industry from British ambassador in Switzerland Clifford Norton
US reports from Bern on German war industry
The messages in the Finnish archives were located and copied for me by the researcher Martti Kujansuu.