William Wirt Gilmer (May 21, 1863 – January 8, 1955) was a United States Navy Captain who served as both the 22nd and 24th Naval Governor of Guam.

A graduate of the United States Naval Academy, he commanded the USS South Carolina during World War I, for which he received the Navy Cross.

He exercised a large amount of control over islanders' daily lives, including banning whistling and smoking and setting up a curfew.

He came into conflict with prominent Americans and Washington Naval leaders when he outlawed marriage between whites and non-whites on the island, believing the Chamorro people inferior.

[6] A month before he arrived, Guam experienced an outbreak of influenza, and though he set up quarantine zones upon taking command, the pandemic lasted through December, with nearly a thousand dead.

[8] Gilmer attempted to justify his order to the committee in 1919 by claiming that "if a man in the United States marries a woman of any other color, he sinks immediately to the level of his wife.

"[9] James H. Underwood, postmaster of the island, wrote directly to officials in Washington, D.C. to protest the move, as many Americans had already married Chamorros.

He eventually obtained a meeting with the Chief of Naval Operations, former Guam governor Robert Coontz,[8] and soon after Franklin D. Roosevelt, then Assistant Secretary of the Navy, personally wrote to Gilmer and ordered the law revoked, allowing whites to again marry Chamorros and Filipinos.

[6] In March 1920, Gilmer began requiring that all men sixteen and older obtain a cèdula personal, essentially an identification document issued by the government.