What presidents had the highest military rank?

Answer 1

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.

Answer 2

George Washington, Andrew Jackson, William Henry Harrison, Zachary Taylor, Ulysses S. Grant, Rutherford B. Hayes, and Dwight D. Eisenhower all attained the rank of general before becoming President of the US. Other US presidents held lesser military ranks.