Unfortunately, separation and divorce affect U.S. Servicemembers as well as the public. Many military spouses lack the ability to retain legal counsel and may resort to a Do-It-Yourself Kit. I do not recommend this for many reasons.
If a military spouse can afford counsel, counsel still has to make service of process on the SM. If this is a simple case--for example, a 1-year marriage, no assets, no children, no support case--service of process may be informal simply because both parties want to end the marriage. The defendant service member may be cooperative in ending the marriage. The judgment would have to include a provision that states that the servicemember was advised of his/her rights under the Servicemembers Civil Relief Act and intentionally, knowingly waived those rights.
If, however, there are children involved in a divorce or if the parties never married but paternity needs to be established, informal service of process will not be advisable. The party seeking a court order needs to know that the order or orders will be enforceable later and will not be subject to attack.
Here are two important tools explaining possible ways in which service of process may occur. This is complicated, so a lawyer will need to be involved.
How to Make Service of Process on Active Duty U.S. Service Members: Service of Process - Military - Child Support, a Training Program. This is for cases involving establishment of support orders, establishment of paternity, etc.
Download Service of Process - Military - Child Support
Service of Process - Military - Fort Irwin Memo Child Support, Family Support, Paternity
This memo explains in general how to service process in cases involving establishment of support orders, establishment of paternity, etc.
Be mindful that the Servicemembers Civil Relief Act protects active duty service members from civil suits. See this earlier blog post: How SCRA Protects Servicemembers from Foreclosures & Civil Suits
Or buy the book. Sullivan, Mark E. The Military Divorce Handbook: A Practical Guide to Representing Military Personnel and Their Families (2nd Edition). American Bar Association, 2013.