What presidents had the highest military rank?

Given that the highest rank possible in the US Military is Commander-in-Chief, and that the Commander-in-Chief is the President, they all held the highest rank possible.

THE ABOVE answer I found here is incorrect. The Commander-in-Chief position is civilian, not military. The whole point of making the president C-in-C is to have civilian control of the military, unlike in other countries in the 18th century whose military did not answer to the government. The president is not a member of the military. I am told George Washington was the only six star general in history (before being president, of course), but I have not checked.