[1] He also was an equivalent graduate of the National War College and is credited with starting the Non-Commissioned Officers Academy system.

In the Second World War, as a colonel and then a brigadier general, he commanded Combat Command A (CCA) of the 4th Armored Division in General George S. Patton's Third Army, leading it to victory over a superior German armored force at the Battle of Arracourt in September 1944.

In December Clarke led the relief of St. Vith during the Battle of the Bulge, which slowed the German attack.

On 18 October 1971, the Supreme Council of the Scottish Rite for the Southern Jurisdiction of the United States conferred upon Clarke, a 33rd Degree Freemason, the Grand Cross of the Court of Honor.

He also received decorations from foreign countries including France, Germany, Great Britain, Korea, and the Philippines.

[2] Clarke died after a stroke on 17 March 1988, at Walter Reed Army Medical Center and was buried with full military honors in Section 7-A (Grave 130) at Arlington National Cemetery.