Ronda Rousey: Arrives to Marine Corps Ball ... Let's Kick It!

Ronda Rousey's the belle of the Marine Corps Ball -- arriving to the big bash in South Carolina moments ago ... to keep her promise to Lance Corporal Jarrod Haschert.

Ronda flew out early Friday morning -- and to be honest, still seemed pretty down in the dumps nearly one month after losing to Holly Holm.

But she was all smiles at the ball -- posing for pics with the marines and their dates -- and hopefully, enjoying herself.

Ronda's gonna need to get her mojo back if she's gonna have a chance to beat Holm in the rematch -- and who better to help reclaim her swagger than a buncha devil dogs, right?!?

Oorah!