World War I

In the summer of 1913, Nimitz (who spoke German) studied engines at the diesel engine plants in Nuremberg , Germany, and Ghent , Belgium.
Returning to the New York Navy Yard , he became
executive and engineer officer of Maumee at her commissioning on October 23, 1916.
After the United States declared war on Germany in April 1917, Nimitz was Chief Engineer of Maumee while the vessel served as a refueling ship for the first squadron of U.S. Navy destroyers to cross the Atlantic, to take part in the war. Under his supervision, Maumee conducted the first-ever underway refuelings. On August 10, 1917, Nimitz became aide to Rear Admiral Samuel S. Robison , Commander, Submarine Force, U.S. Atlantic Fleet (COMSUBLANT ).
On February 6, 1918, Nimitz was appointed chief of staff and was awarded a Letter of Commendation for meritorious service as COMSUBLANT's chief of staff. On September 16, he reported to the office of the Chief of Naval Operations, and on October 25 was given additional duty as Senior Member, Board of Submarine Design.
Between the wars
From May 1919 to June 1920, Nimitz served as executive officer of the battleship South Carolina . He then commanded the cruiser Chicago with additional duty in command of Submarine Division 14, based at Pearl Harbor , Hawaii. Returning to the mainland in the summer of 1922, he studied at the Naval War College, Newport, Rhode Island .
In June 1923, he became aide and assistant chief of staff to the Commander, Battle Fleet , and later to the Commander In Chief, United States Fleet . In August 1926, he went to the University of California, Berkeley, to establish the Navy's first Naval Reserve Officer Training Corps unit.
Nimitz lost part of one finger in an accident with a diesel engine, only saving the rest of it when the machine jammed against his Annapolis ring.[10]
In June 1929, he took command of Submarine Division 20. In June 1931, he assumed command of the destroyer tender Rigel and the destroyers out of commission at San Diego, California . In October 1933, he took command of the cruiser Augusta and deployed to the Far East , where in December, Augusta became the flagship of the Asiatic Fleet .
In April 1935, Nimitz returned home for three years as assistant chief of the Bureau of Navigation, before becoming commander, Cruiser Division 2, Battle Force. In September 1938. he took command of Battleship Division 1, Battle Force. On June 15, 1939, he was appointed chief of the Bureau of Navigation. During this time, Nimitz conducted experiments in the underway refueling of large ships which would prove a key element in the Navy's success in the war to come.