As of the 2016 election, 29 American presidents served in the U.S. Armed Forces. The last sitting president to have served his country prior to taking the nation's highest office? George W. Bush.

There must be a correlation between serving in the armed forces and leading the nation since over half of all the U.S. presidents have served in the armed forces. Considering that the commander-in-chief is also the head of the military, it makes sense that voters consider a would-be president's military experience before casting their ballots. However, serving in the military isn't a requisite for becoming president of the United States.

The most common branch of the military where a future president has served is the Army or Army Reserve, followed by State Militia, Navy/Naval Rescue, and Continental Army. To date, no president has spent time serving in the U.S. Marine Corps or the U.S. Coast Guard.

Brush up on your knowledge of presidential military history, then check out these other shocking things you didn't know about American presidents.

Presidents Who Served in the Army

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To date, 15 presidents have served in the Army or Army Reserves.

Ronald Reagan

Ronald Reagan enlisted in the Army Reserve during World War II. He was ordered to active duty in 1942, but because of his limited eyesight he was excluded from serving overseas for the duration of his enlistment. He was separated from active duty in 1945.

Dwight Eisenhower

President Eisenhower graduated from the U.S. Military Academy at West Point in 1915. He served the military until 1948 and is perhaps most well known for his role in executing Operation Overlord on what's now known as D-Day.

Harry S. Truman

President Truman had originally been in the Army Reserves from 1905–1911 and decided to reenlist once the U.S. entered World War I. He was promoted to Captain in 1918 and was honorably discharged from the Army a year later. He remained a reservist until 1953.

Theodore Roosevelt

Theodore Roosevelt served in the Army during the Spanish-American War and was a so-called Rough Rider. He is the only president to have ever won the Medal of Honor. It was awarded posthumously in 2001.

William McKinley

President McKinley served in the Civil War under future President Rutherford B. Hayes. He was the last president to serve in the Civil War and was assassinated just six months into his presidency.

Benjamin Harrison

Benjamin Harrison was a Union soldier during the American Civil War. He was originally just a recruiter for the Army but eventually was promoted to Command and then Brevet Brigadier General.

James Garfield

President Garfield was also a Brigadier General during the American Civil War and fought on the Union side. He left the Army to serve in the U.S. House of Representatives and eventually became president. He was assassinated six and a half months into his presidency.

Rutherford B. Hayes

President Hayes was seriously wounded when he was fighting in the American Civil War as a member of the 23rd Ohio Infantry. He was promoted to Brevet Brigadier General and commanded future president William McKinley.

Ulysses S. Grant

President Grant served in both the Mexican-American War and the Civil War. He's better known for his role as Commanding General for the Union Army in the American Civil War.

Andrew Johnson

Andrew Johnson served in the Tennessee Militia and then in the Civil War. President Johnson is better known for being just one of two presidents to have ever been impeached. (The other is President Bill Clinton.)

Franklin Pierce

President Pierce served in the Mexican-American War and was a member of the New Hampshire militia from 1831–1846.

Zachary Taylor

President Taylor's military career spanned from 1808 until 1848. During that time, he served in the War of 1812, Black Hawk War, Second Seminole War, and Mexican-American War.

William Henry Harrison

President Harrison served in the Northwest Indian War and the War of 1812. He achieved the rank of Major General.

Andrew Jackson

President Andrew Jackson served in several wars during his time in the U.S. Army: the Revolutionary War, the War of 1812, the Creek War, and the Seminole War.

George Washington

Our first president, George Washington, led troops during the Revolutionary War and the French-Indian War.

Presidents Who Served in the State Militia

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The U.S. used to rely heavily on state militias. To date, nine presidents have served in state militias. Some served in both state militias and the national army.

Chester A. Arthur

President Arthur served in the New York State Militia during the Civil War and was commissioned as Brigadier General. He succeeded President Garfield after his assassination in 1881.

Abraham Lincoln

President Lincoln served as Captain in the Illinois State Militia during the Black Hawk War.

James Buchanan

President Buchanan enlisted as a private in the Pennsylvania State Militia in 1814. He is the only president to have served in the armed forces who never served as an officer.

Millard Fillmore

President Fillmore served in the New York Militia during the 1820s and 1830s and was promoted to General.

James K. Polk

President Polk joined the cavalry unit of the Tennessee Militia and was later promoted to Captain.

John Tyler

President Tyler served as Captain of the Virginia Militia during the War of 1812.

James Madison

James Madison served in the Virginia Militia during the American Revolution. He later commanded troops during the War of 1812.

Thomas Jefferson

President Jefferson was a member of the Virginia Militia and commanded the Albemarle County militia during the start of the Revolutionary War.

Presidents Who Served in the Navy and Air Force

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The smallest grouping of presidents served with the Navy and Air Force. Though the Air Force was founded in 1947 and could explain the smaller showing, the Navy was founded in October of 1775, just four months after the founding of the U.S. Army.

George W. Bush

George W. Bush served in the Texas Air National Guard and was a stateside pilot during the Vietnam War.

George H.W. Bush

Leading the way for his son, President Bush Sr. served as a naval aviator in the U.S. Navy during World War II.

Jimmy Carter

President Carter served in the U.S. Navy during World War II and the Korean War.

Gerald Ford

President Ford served as Lieutenant Commander in the U.S. Naval Reserves during World War II. He was discharged in 1946.

Richard Nixon

President Nixon served in the U.S. Naval Reserves during World War II, earning two battle stars for his service in the Pacific.

Lyndon B. Johnson

President Johnson, aka Light Bulb Johnson, served as a Commander in the U.S. Naval Reserve during World War II.

John F. Kennedy

President Kennedy served in combat as Lieutenant in the U.S. Naval Reserve during World War II. He earned the Purple Heart award.