A military wedding can mean different wardrobe choices. There are informal military weddings. Most military wedding I’ve seen have meant the men are in their “dress blues” or “blue or white mess dress” which means they are in their fancy uniforms.
If this is what the guys are wearing, don’t show up in your maxi dress. When the men are wearing something sharp, now is not the time to look frumpy.
For a military wedding, I think something with structure is appropriate. I like these retro inspired dresses with the full skirts. They have seaming and shape up top and are a little flirty and feminine on the bottom.
A little bit of the same structure he’s wearing, a little bit girly. A perfect match to salute that arch of swords!