Service Requirements for the Navy HPSP?

I'm currently taking pre-med classes and have looked into the Navy's Health Professional Scholarship Program (HPSP) to help pay for my medical school education. For anyone who has experience with it: I understand that there's a service requirement of 5 years to which your residency does not count. What do they mean by 'service requirement'? I'm planning on going for pediatrics and I can't imagine they'd have much use for a pediatrician on an aircraft carrier in the middle of the ocean so is this just additional time I have to spend at a naval hospital on top of my residency or do they expect me to go out into the fight and stitch up kids?