Dear Ms. Dimitrakopoulou,
Thank you for posting your request on History Hub!
Since the United States did not officially fight in WWII until December 7, 1941, the only statistics we would have may be in correspondence or dispatches from the United Kingdom and other countries.
We searched the National Archives Catalog and located a series titled The Franklin D. Roosevelt/Winston Churchill Correspondence, 1939 - 1945 in the Papers as President, Map Room File, 1939 -1945 (Collection FDR-MR) that includes correspondence between President Roosevelt and Winston Churchill from the outbreak of World War II in Europe. For access to these records, please contact the Franklin D. Roosevelt Library (LP-FDR) via email at firstname.lastname@example.org.
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from LP-FDR. We apologize for this inconvenience and appreciate your understanding and patience.
For the information you seek, please contact the National Archives of the nations that were involved in WWII during 1939 such as the British Imperial War Museum; the National Archives of France (Archives Nationales); the Bundesarchiv Abt. VI - Militärarchiv of Germany; the Federal Archival Service of Russia; and the National Archives of Poland.
We hope this is helpful. Best of luck with your research!