One great resource available from the U.S. National Archives is the World War II Enlistment Records. These records have been transcribed and made available on the National Archives web site. These records are especially valuable as many of the personnel papers of these soldiers and sailors were later destroyed in a fire.
The National Archives scanned War Department microfilmed punch cards on enlistments to support the reconstruction of the military personnel records at its National Personnel Records Center. That strikes me as a sad commentary about technology: the data was originally stored on punch cards which, once upon a time, could be read by machines. I haven't seen a punch card reader in operation for many years, however. The cards were eventually microfilmed for long-term preservation.
Nine million records were later transcribed manually by humans who sat and read the microfilms and transcribed the information onto keyboards. Due to the condition of the microfilms, approximately 1.5 million records could not be scanned. Scanning problems when the microfilms were created also contributed to the errors. Despite these challenges, information about a majority of sixteen million World War II servicemen and women is available via the web site.
I went to the web site and did a search for an uncle of mine. Thanks to his unusual last name, he was easy to find: he was the only person of that name in the database. Finding him took less than a minute. Looking for someone with a more common surname will take longer, but you can use the site's "Advanced Search" to use Boolean terms. For instance, all the men named Jones who enlisted in Maine or something similar.
The final record that I was able to see was a transcribed entry, not an image of an original form. That's okay in this case because the online transcriptions were made from another transcription: the original punch cards that were made from original records. In other words, I was looking at a transcription of a transcription.
The U.S. National Archives says spot checks show that approximately 35% of these records have an error. However, only 4.7% of the sample had an error in the name column, and only 1.3% had errors in the serial number column. Therefore, the National Archives made the determination that a lot of valuable information is available in this database, even with the errors. The database was released and placed online.
I didn't notice any errors in the data I saw about my uncle and about a few others that I found.
Each record provides the enlistee's serial number and name, state, and county of residence, place of enlistment, date of enlistment, grade, branch, term of enlistment, place of birth, year of birth, citizenship, race, education, civilian occupation, marital status, and component. I did see a few items left blank or listed as N/A (not available). However, most of the records I saw were filled in completely.
Because the records are for Army enlistments during World War II, the file does not include records for those who enlisted as Army officers. It does, however, have records for those who joined as enlisted personnel and then later were promoted to commissioned officers, as in the case of my uncle. Just because your relative served as an officer, do not assume that he or she is not in this database. The question is, what was the grade upon enlistment, not on discharge?
This online database also contains information on more than 130,000 women who enlisted in the Women's Army Auxiliary Corps.
The Electronic Army Serial Number Merged File can provide much information of interest to genealogists. It is especially useful for date and place of birth, even though it does not show parents' names. At least you will find out where to look for a birth record.
The Electronic Army Serial Number Merged File is available free of charge as one of the databases within the U.S. National Archives and Records Administration's "Access to Archival Databases" (AAD) at http://www.archives.gov/aad.