Thank you for your message, and welcome to our Forum. Unfortunately, since we are in no way linked to or affiliated with the US Army or Government, it can be extremely difficult for us to provide detailed information regarding the service of WW2 personnel.
I did a search of your Grandfather's name in the National Archives Enlistment database , but unfortunately there are several servicemen named William H. Wilson listed therein. I wonder if you may be able to narrow down the individual record that relates to your Grandfather from the results found at the address below:NARA Records
As you may be aware, a large fire at the National Archives' St. Louis facility in 1973 destroyed many of the WW2 US Army Enlistment Records, and most have been irreplaceable. That having been said, it may still be worthwhile contacting the US National Archives () to check whether any documents or records are held of your Grandfather, or indeed his unit.
I hope that the above information may be of some interest to you, and I am sorry that we cannot assist further with your query at this time.