How do you put up with very little sleep?

I am in the Sea Cadets. I like to get up early, I like the early morning. Its just sometimes, at home, I don't even get up in the early morning and then I feel bad I slept in... Sometimes when I wake up, I don't really even think, I just turn off my alarm clock and fall back asleep, then later when I really wake up I remember.. And at sea cadets when we get up at 4 or 5am, I really feel horrible(which is understandable). Any tips on NOT feeling so tired? And any tips on at least thinking straight when so tired? And any tips on waking up early? Please help.