Where is the U.S. Third Fleet headquarters located?

The correct answer is San Diego, California. The U.S. Third Fleet is primarily based in this city, which serves as a vital hub for naval operations in the Pacific region. San Diego's strategic location on the West Coast allows the Third Fleet to effectively execute its mission regarding maritime security, crisis response, and cooperative training exercises with international partners.

The Third Fleet's responsibilities include managing naval forces in the Pacific and providing essential support to various operations and exercises. San Diego, with its well-equipped ports and proximity to Pacific shipping lanes, is well-suited for the fleet's operational needs.

The other locations listed do not serve as the headquarters for the Third Fleet. Pearl Harbor is home to the U.S. Pacific Fleet but is not the command center for the Third Fleet. Seattle, while an important naval city, does not house the Third Fleet's headquarters. Guam is strategically significant for U.S. military operations in the Asia-Pacific but is not the administrative center for the Third Fleet.