The official answer to this common question is provided by the website of the National Personnel Records Center.
41 years ago on July 12, 1973, a disastrous fire at the National PersonnelRecords Center (NPRC) destroyed approximately 16-18 million Official Military Personnel Files (OMPF). The records affected were:
Personnel and Period
Affected
|
Estimated Loss
|
|
Army
|
Personnel discharged November 1, 1912 to January 1, 1960
|
80%
|
Air Force
|
Personnel discharged September 25, 1947 to January 1, 1964
(with names alphabetically after Hubbard, James E.) |
75%
|
In addition, one's local library may subscribe to the Ancestry.com Library Edition which links to an Ancestry Anne blog entry which lists available collections of American military records and explains why one's relative may not yet show up in World War II Draft Registration cards.