Presidents with military service records

I was talking with a co-worker yesterday about Prince Harry's probable deployment to Iraq. We were talking about the the difference between the British Royalty and the off-spring of our own elected officials. I rather jokingly doubted that any U.S. President would have sent his own son into Iraq.

Of course, it isn't equitable to compare British Royalty to our own president. I'm not trying to argue that one way or another.

It did lead us to a conversation about the tradition of British Royalty to enter military service as compared to America's leaders. I disgustingly commented that it's been a while since we've had a leader with real military knowledge under his belt.

History does not long entrust the care of freedom to the weak or the timid. - Dwight D. Eisenhower

So, the question I had was how many U.S. Presidents had active military service (G.W. doesn't count) and what kind of record does the British Royalty have as well?