Military ball

Hi ladies! So my new boyfriend invited me to his military ball and I’m not really sure what kind of dress to wear. Long? Short? Sleeves? Sleeveless? Slit in the skirt? Tight dress? I’ve googled it and I’m not really sure what’s considered appropriate for this event. Please help!?! Maybe put pictures so I can get some ideas? Thanks so much ❤️

**update**

So I’ve tried what feels like, every store out there... Macy’s, jcp, lord and Taylor, Windsor . I’m not sure where else to go. Any suggestions?