Well, Shirou, I'm not too clear on that myself. I know it has something to do with condoms, which are useful for carrying a liter of water in the jungle, and also with kissing, which is like mouth-to-mouth resuscitation. So I assume it's a special tactical drill that will help replenish energy and health in the field.
Though, whenever those girls get close to me, I get a funny feeling run through my body, and somehow, I think its related to sex. But I can't see how that nervous feeling could help my combat ability, so it must not be related. Just a stupid thought. Oh well.