The WWI and WWII Registration or Enlistment records are a genealogists gold mine that many people do not know about. Make sure you check for you ancestor because you will get the following info
1. Full Name (one of the few records with a middle name)
2. Date of Birth
3. County and State of Birth
4. If the ancestor is single or married with dependents (great information)
5. Where they work and for whom?
6. If they have anything wrong with them physically to keep from serving
7. Hair Color, Skin Color, Height, Weight
I have found these to be great musts for any searcher.
The WWII is perfect because the latest census is 1930 and this puts that ancestor in a location to do research in.
Ancestry.com has all the records and you can physically view them. If you are not a member, I am more than happy to look it up for you. I love the military records since my own step father who raied me was a very decorated Vietnam Vet
I have attached two records you can see how these can be such a help in your search