Lieutenant William Thomas Fitzsimons (April 18, 1889 – September 4, 1917) was an American physician and United States Army officer in World War I, and is considered the first American officer killed in the war.

When the U.S. entered World War I, Fitzsimons was called into active duty.

He volunteered for overseas duty and left Kansas City on June 14, 1917.

[1] Fitzsimons was killed in a German air raid on September 4, 1917 along with Pvt.

He was laid to rest in the afternoon of September 5, 1917 with full military honors in the British cemetery at Etaples along with the three enlisted men who also perished.