One of our President's seven main duties is that of Commander in Chief of the U.S. Armed Forces. Essentially the be-all-end-all of every major military decision. From the signing peace treaties with Britain in the late 1700s to the decision to remain in Iraq in 2008, the President is the highest military authority.
This being said, serving in the military is not a pre-requisite to become President, although more than half of our Presidents have done so.
In these times of change, Republican front-runner, John McCain's military background is being seen by some as a competitive advantage. And if elected it could very well impact his decision making. A recent article on McCain in Newsweek highlighted this fact and also took a closer look at six presidents who's military service have had a particular impact on them. According to historian Michael Beschloss)
George Washington
Top Military Rank: General
Active Service: American Revolutionary War, French and Indian War
Branch: Virginia Militia, Continental Army
After successfully winning the Revolutionary War, Washington knew Britain still posed a serious threat, and thus signed an unpopular treaty with Britain protecting the United States from British invasion.
Andrew Jackson
Top Military Rank: Major General
Active Service: American Revolutionary War, War of 1812, Creek War, First Seminole War
Branch: Continental Army, United States Army
Known to many as the guy on the $20 dollar bill, Andrew Jackson learned a great lesson from standing up against and defeating the monstrous British Army. It gave him the courage to take on other big foes like the U.S. Bank. Although it also gave him the confidence to stomp out the innocent Cherokees and force them to move West, killing over 4,000 Cherokees on the Trail of Tears.
Theodore Roosevelt
Top Military Rank: Colonel
Active Service: Spanish-American War
Branch: United States Army
Victory in the Spanish-American War made Roosevelt a national hero. He snowballed this fame into a successful political career, catapulting him to President. Roosevelt definitely used his personality to his advantage and for that is one of our most popular Presidents. His victory in the war, giving the US control over Puerto Rico, Guam and the Philippines also set the stage for American Imperialism impacting much more than just Teddy's Presidency.
Roosevelt was also the only U.S. President to receive the Medal of Honor (awarded posthumously in 2001).
Dwight D. Eisenhower
Top Military Rank: General
Active Service: Stateside service during World War I, Supreme Allied Commander in Europe during World War II, military career lasted from 1915 to 1952.
Branch: United States Army
John F. Kennedy
Top Military Rank: Lieutenant
Active Service: World War II
Branch: United States Navy
George H.W. Bush
Top Military Rank: Lieutenant
Active Service: World War II
Branch: US Navy Reserve
Though there are only six presidents highlighted in the McCain article, there are several other's who's time in the military impacted their presidency. I've taken the time to do some of my own research to find them.
Experts, traditionally view Grant as a President in the bottom quadrant of US Presidents, mostly because of his tolerance of corruption. Grant would often tolerate financial and political corruption among top aids, seemingly unaware of the consequences to those that were being cheated. Though an honest man, Grant appears to have no heart when it comes to the well-being of others.
Carter did post-graduate work, studying nuclear physics and reactor technology for several months in 1953. This followed Carter's first-hand experience as part of a group of American and Canadian servicemen who took part in cleaning up after a nuclear meltdown at Canada's Chalk River Laboratories reactor.
Top Military Rank: Colonel
Active Service: World War I
Branch: US Navy Army/Army Reserve