Dear Mr. Welch,
Thank you for posting your request on History Hub!
We are unaware of any source which compiles statistics on the total number of mid-air collisions that occurred during World War II. The United States Air Force Statistical Digest World War for World War II provides statistics on the numbers of US Army Air Force aircraft accidents during the war, but does not break the numbers down by the type of accident. Aviation Personnel Fatalities in World War II provides statistics about naval aviation personnel killed by accidents but does not give the number of accidents or specify the type of accidents.
The National Archives at College Park - Textual Reference (RDT2) has custody of naval aircraft accident reports for the World War II period among the general correspondence of the Records of the Bureau of Aeronautics (Record Group 72). Aircraft accident reports provide information about accidental losses of Navy aircraft; they do not usually include information about losses of aircraft as a result of Navy war operations or combat engagement. These are almost exclusively losses that occurred in the United States and in US territories. Accidents occurring while deployed may be found in squadron records in the Records of the Chief of Naval Operations (Record Group 38). For more information about these records, please email RDT2 at email@example.com.
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 RDT2. We apologize for this inconvenience and appreciate your understanding and patience.
World War II Army Air Force and Air Force accident reports up to 1955 are in the custody of the Air Force Historical Research Agency, 600 Chennault Circle, Building 1405, Maxwell Air Force Base, AL 36112-6424. The web site is https://www.afhra.af.mil/. These records do not include losses occurring during combat.
We hope this information is helpful. Best of luck with your research!
[some information provided by Nate Patch, Subject Matter Expert]