Post war: On November 26, 1945,

On November 26, 1945, Nimitz's nomination as Chief of Naval Operations (CNO) was confirmed by the U.S. Senate, and on December 15, 1945, he relieved Fleet Admiral Ernest J. King . He had assured the President that he was willing to serve as the CNO for one two-year term, but no longer. He tackled the difficult task of reducing the most powerful navy in the world to a fraction of its war-time strength, while establishing and overseeing active and reserve fleets with the strength and readiness required to support national policy.
For the postwar trial of German Grand Admiral Karl Dönitz at the Nuremberg Trials in 1946, Nimitz furnished an affidavit in support of the practice of
unrestricted submarine warfare, a practice that he himself had employed throughout the war in the Pacific. This evidence is widely credited as a reason why Dönitz was sentenced to only 10 years of imprisonment. [11]
Nimitz endorsed an entirely new course for the U.S. Navy's future by way of supporting then-Captain Hyman G. Rickover 's chain-of-command-circumventing proposal in 1947 to build
USS Nautilus, the world's first nuclear-powered vessel. [12] As is noted at a display at the Nimitz Museum in Fredericksburg, Texas: "Nimitz's greatest legacy as CNO is arguably his support of Admiral Hyman Rickover's effort to convert the submarine fleet from diesel to nuclear propulsion."
From 1949 to 1953, Nimitz served as UN-appointed Plebiscite Administrator for
Jammu and Kashmir.[13] His proposed role as administrator was accepted by Pakistan but rejected by India.