After college, Thomas spent five years at sea before joining the Navy's Judge Advocate General's Office in 1919 in Washington, D.C.. In DC, he studied law at George Washington University Law School where in 1922 he earned his law degree. Gatch then went back to active duty aboard a ship, before teaching for three years at the Naval Academy. In 1935, he returned to the JAG's headquarters where he remained through 1938. Gatch then returned to sea until 1940. That year he began serving as Assistant Judge Advocate General, keeping that post until February 1942 after World War II began. Gatch then became commander of the, a battleship. Serving in the South Pacific until December 1942, commanding the South Pacific in the Pacific Theater of Operations in battles such as the Battle of the Santa Cruz Islands during the Guadalcanal campaign. He received two Navy Crosses for his service. Gatch's time in command was not without controversy. He was, correctly or incorrectly, blamed for a number of incidents involving his command; the grounding of his ship in Tonga in mid-1942, his collision with the destroyer in late 1942, and the inclusion in his crew of a 12-year-old boy - Calvin Graham - who was wounded during the Guadalcanal campaign. While Gatch's time in command was not without victory and success, his reports were often criticized for gross exaggerations of success. Gatch's actions during the Naval Battle of Guadalcanal included a fateful decision to initially engage the Japanese battleship Kirishima with his secondary battery only. During the subsequent fighting, the South Dakota suffered significant casualties, among them Gatch. Gatch was injured by shell splinters when the bridge of the South Dakota was struck by shells from the Kirishima. In 1943 Gatch was invalided to shore duty, officially due to his wounds. Gatch became the 16thJudge Advocate General of the United States Navy. He remained in that position until December 3, 1945, when he became the commander of the service force of the Atlantic Fleet. Vice Admiral Thomas Leigh Gatch retired from the Navy in 1947.
Later life and family
From 1945 to 1947 he served as a trustee at George Washington University. Thomas had one sibling, Orytha. He would have three children with his wife; Thomas Leigh Gatch, Jr., Nancy, and Eleanor. His son Thomas, Jr. attended the United States Army’s service academy at West Point and disappeared in 1974, whilst attempting the first crossing of the Atlantic Ocean by balloon. After retiring from the Navy, Gatch returned to his native Oregon. Thomas L. Gatch died on December 16, 1954, in San Diego, California, and is buried there at Fort Rosecrans National Cemetery.