Washington, DC. Krueger worked on the United States color-coded war plans, particularly War Plan Green, for another war with Mexico, and War Plan Blue, for another civil war in the United States. He traveled to the Panama Canal Zone in January 1923 to report on the state of the defenses there. After he returned, he was assigned to the Joint Army and Navy Planning Committee, an organ of the Joint Army and Navy Board responsible for coordinating war plans between the two services. While with the Joint Planning Committee, he worked on War Plan Orange, the plan for a war with Japan, and War Plan Tan, for a war with Cuba. Krueger considered the problems of inter-service cooperation. At his own request, he attended the Naval War College at Newport, Rhode Island, in 1925 and 1926. He continued to ruminate on the nature of command. "Doctrine", he wrote, "knits all the parts of the military force together in intellectual bonds." Krueger came to feel the prospects for promotion in the infantry were very poor, and in 1927 he tried to transfer to the United States Army Air Corps. He attended the Air Corps Primary Flying School at Brooks Field, Texas, but suffered an attack of neuritis in his right arm, and his flight instructor, Lieutenant Claire Lee Chennault, failed him. In December 1927, he was offered a position as an instructor at the Naval War College, where he taught classes on World War I, and on joint operations. In June 1932, Krueger became commander of the 6th Infantry Regiment at Jefferson Barracks, Missouri, where he was promoted to colonel again on 1 August 1932. Now aged 51, he became resigned to retiring as a colonel, but in 1934 he returned to the War Plans Division, becoming chief of the division in May 1936, and was promoted to temporary brigadier general in October 1936. In September 1938, Krueger went to Fort George G. Meade, Maryland, as commander of the 16th Infantry Brigade. He was promoted to temporary major general in February 1939, when he became commander of the 2nd Infantry Division at Fort Sam Houston, Texas. The 2nd Infantry Division was at the time being used as the Proposed Infantry Division (PID). With Lesley J. McNair as commander of the 2nd Division Artillery and chief of staff of the PID, the PID tested of the US Army's new triangular division concept.