It's the crew (staff) of HMS Ocean, a British warship, singing/mimeing Mariah Carey's 1992 hit All I Want for Christmas.
I love it. Makes me feel happy.
The ship left the Uk in April for a 7 weeks training time, but because of events in Libya this summer it was diverted and is only coming back to Plymouth now.
When the crew heard that they would be "home for Christmas" they came up with the idea of making this video...
British sense of humour: we love dressing up (or down!), making fools of ourselves and looking un-cool.
I hope you enjoy the video too.