Dear Mr. Richards,
Thank you for posting your request on History Hub!
If this is in regard to a recent casualty, we suggest contacting the Department of Defense’s Casualty Assistance Program to inquire as to whether the military has any information about the will. There are also various websites that offer advice in locating wills, such as How to Get a Copy of a Will.
In regards to historical casualties, the National Archives does not have copies of wills created by service members. If the soldier registered his will with a local courthouse prior to his deployment, or if the family submitted the will to a probate court after his death, the court may have a copy. For more information, see the FamilySearch Wiki page on United States Probate Records. Otherwise, the will would have remained in private custody, to be retained or disposed of at the discretion of whomever ended up with it. In a minority of cases, the family may have donated the will and other personal papers to an institution such as a library or a historical society.
We hope this is helpful. Best of luck with your research!
Approximately what was the date of death (month and year) and what city/county/and state are applicable?