Ahem, I can confirm that mass nudity is an occasional pastime for most of HM Forces. The sport of 'naked fire jumping' for example is one that I can recommend to the young and hardly sober.
The difference with the Royal Marines, I found, is that the tattoos tend to be more lurid and there tends to be a more intense fascination with various types of lingerie in conjunction with the nakedness thing. We won't mention the roll mat thing.... ;D