As a junior at Adair County High School, he received an appointment to the United States Naval Academy at Annapolis from Congressman Ralph Gilbert, to begin in 1925.

However, Gilbert revoked the appointment after traveling to the Far East that summer on a Navy cruiser and being appalled by what he considered to be excessive drinking by the ship's officers during port calls.

Hamlett spent the intervening year at Lindsey Wilson Junior College and entered the Military Academy on 1 July 1926, where he roomed with future four-star general Hamilton H. Howze.

He abandoned the Air Corps upon receiving his desired assignment as a gunnery instructor at the field artillery school at Fort Sill.

At Army Ground Force Headquarters, Hamlett's first assignment was to write the manual on corps artillery doctrine, based on his observations in North Africa.

The division saw light action in Germany and advanced into Czechoslovakia, liberating Plzeň before being ordered to halt short of Prague.

[5][6] In December 1949, Hamlett was ordered to the headquarters of General of the Army Douglas MacArthur as executive officer of the logistics section (G-4), GHQ, Japan.

Tensions escalated as the Soviets began interfering with Western access to Berlin by detaining United States convoys on the autobahn for hours.

On 2 November, as chairman of the three-power Allied Kommandatura for that month, Hamlett informed his Soviet counterpart that should the East Germans attempt to fly the flags in the Western sector, then West German police would remove them, and that should the police be prevented from removing the flags, then Allied troops would complete the job and hold the Russians responsible for any resulting disorder.

[10] Five days later, the army announced that Hamlett had been reassigned to Washington, D.C., stressing that the move was a long-scheduled rotation since the crisis had already extended his tour six months beyond the normal two years.

[12] As vice chief of staff, Hamlett negotiated the creation of United States Strike Command with Air Force chief of staff General Curtis LeMay, played a key role in army operations during the Cuban Missile Crisis, and participated in the escalation of the Vietnam War.

I think it was a failure, and I would have to say that I shared the responsibility because I didn't see far enough ahead to speak out".Hamlett was receptive to dissenting views about the progress of the war, most notably arranging for Lieutenant Colonel John Paul Vann to brief the Joint Chiefs of Staff (JCS).

A week later, Vice Chief of Naval Operations Admiral Claude V. Ricketts also suffered a heart attack and actually did die.

Detecting a trend, Air Force vice chief of staff General William F. McKee visited Hamlett in the hospital and announced his own retirement.

The Vermont College student body was predominantly women, sparking apprehension that Norwich might lose its military character.