From 1920, Eisenhower served under a succession of talented generals – Fox Conner, John J. Pershing, Douglas MacArthur and George Marshall. He first became executive officer to General Conner in the Panama Canal Zone, where, joined by Mamie, he served until 1924. Under Conner's tutelage, he studied military history and theory (including Carl von Clausewitz's On War), and later cited Conner's enormous influence on his military thinking, saying in 1962 that "Fox Conner was the ablest man I ever knew." Conner's comment on Eisenhower was, "[He] is one of the most capable, efficient and loyal officers I have ever met." On Conner's recommendation, in 1925–26 he attended the Command and General Staff College at Fort Leavenworth, Kansas, where he graduated first in a class of 245 officers. He then served as a battalion commander at Fort Benning, Georgia, until 1927.