John Smith Thach (April 19, 1905 – April 15, 1981) was a World War II Naval Aviator, air combat tactician, and United States Navy admiral. Thach developed the Thach Weave, a combat flight formation which could counter enemy fighters of superior performance, and later the big blue blanket, an aerial defense against kamikaze attacks.

John S. Thach was born in Pine Bluff, Arkansas, on April 19, 1905. He graduated from the United States Naval Academy in 1927 and spent two years serving in battleships, before becoming a Naval Aviator in early 1930. His USNA classmates included William Brockman, Creed Burlingame, and Eugene Lindsey. Thach spent the next decade serving as a test pilot and instructor and establishing a reputation as an expert in aerial gunnery.

In early 1940, Thach was placed in command of Fighting Squadron Three (VF-3). There he met a young ensign just out of flight school, Edward O'Hare, later a Medal of Honor recipient. Thach made O'Hare his wingman and taught him everything he knew. At the United States Navy fleet gunnery competition at the end of 1940, eight of the 16 VF-3 pilots qualified for the gunnery "E" award ("excellence").

Later Thach developed a fighter combat tactic known as the Thach Weave. This tactic enabled American fighter aircraft to hold their own against the more maneuverable Mitsubishi A6M Zero, the primary Imperial Japanese Navy fighter aircraft.

Lieutenant Commander Thach and VF-3 flew from USS Saratoga in the early part of World War II, and was assigned to USS Yorktown during the Battle of Midway in June 1942. On the morning of June 4, Thach led a six-plane sortie from VF-3, escorting twelve Douglas TBD Devastators of VT-3 led by Lieutenant Commander Lance Massey from Yorktown, when they discovered the main Japanese carrier fleet. They were immediately attacked by 15 to 20 Japanese fighters. Thach decided to use his namesake maneuver, marking its first combat usage. Although outnumbered and outmaneuvered, Thach managed to shoot down three Zeros and a wingman accounted for another, at the cost of one Grumman F4F Wildcat.

After Midway, Thach was assigned to instruct other pilots in combat tactics. The United States Navy pulled its best combat pilots out of action to train newer pilots, while the Japanese kept their best pilots in combat. As the war progressed, the Japanese Navy lost their experienced pilots due to attrition and had no well-trained replacements, while the United States was able to improve the general fighting ability of their own personnel. When the Japanese resorted to the feared Kamikaze suicide attacks, Thach developed the "big blue blanket" system to provide an adequate defense.

Later in the war, Commander Thach became operations officer to Vice Admiral John S. McCain Sr., commander of the Fast Carrier Task Force. Thach was also present at the formal Japanese surrender aboard the battleship USS Missouri on September 2, 1945, in Tokyo Bay.

Thach was a flying ace, having been credited with shooting down six enemy aircraft during World War II.