What to wear?! Help me!

Monique • Mermaid stuck on dry land 🧜🏼‍♀️

My boyfriend is in the Air Force and on the 5th his unit is doing a formal dining in. He doesn’t know much about female civilian dress code. All he said is a floor length formal dress. Anyone else know the dress code I need to follow? I’m at a loss of what I need to know before buying a dress.

Update: everything went really successful and I think we looked pretty great!