(left) with Chamberlin|alt=A man in uniform sits at a desk. He wears three stars and wings on his breast. Another, in a similar uniform but wearing only one star, leans over. In 1938, Chamberlin became Assistant Chief of the Construction Branch in the G-4 Division of
War Department General Staff. At this time, the United States was embarking on a military buildup in response to a worsening international situation, which culminated in the outbreak of World War II on 1 September 1939. A major component of this build up was a vast construction program of arsenals, depots, airbases and coastal defenses. Some $175 million was allocated to construction under the Expansion Program, as it became known. On 7 May 1940, the Assistant Chief of Staff, G-4, Major General Richard C. Moore, G-4 of the War Department General Staff, asked for an estimate of the cost to house an additional 1,200,000 men and balked at the estimate he received of $800 per head. To save on the cost of cantonments, Moore decided not to paint them. Chamberlin disagreed on the grounds that paint would reduce maintenance costs. President
Franklin Roosevelt intervened and directed that the buildings be painted. As a result, an order was placed for of paint, resulting in an $11 million budget shortfall. Chamberlin was promoted to
colonel on 14 February 1941. Chamberlin was promoted to
brigadier general on 15 February 1942. On 19 April, MacArthur formally established his General Headquarters (GHQ), and Chamberlin was appointed its Assistant Chief of Staff, G-3. As G-3, Chamberlin was one of the most highly rated members of the GHQ staff, although not being part of the "Bataan Gang" – the group of officers who had escaped with MacArthur from the Philippines – made him something of an outsider at GHQ. Chamberlin was responsible for planning and overseeing the execution of MacArthur's major operations, including the
New Guinea,
Philippines and
Borneo campaigns. One member of the staff later recalled: Chamberlin jealously guarded his position. In late 1943, Chamberlin differed with one of his planners, Brigadier General
Bonner Fellers, over a proposed landing at
Hansa Bay. Fellers thought that Hansa Bay could be bypassed, but Chamberlin felt that this would be too risky. While Fellers was a newcomer to GHQ, he had known MacArthur for many years, and Fellers took his proposal directly to MacArthur, who approved it. A furious Chamberlin had Fellers fired from G-3. MacArthur made him his military secretary. One of Chamberlin's challenges was working with the Australians. Their decentralized mode of planning was entirely different from the top-down approach used by GHQ, and Chamberlin found this a source of frustration, as it was difficult to extract information from them. Nonetheless, he established a good working relationship with the Australian Deputy Chief of the General Staff, Lieutenant General
Frank Berryman. When MacArthur began looking for a new chief of staff to replace Lieutenant General
Richard K. Sutherland in 1945, he considered but rejected giving the post to Chamberlin. Chamberlin became Deputy Chief of Staff in February 1946, and was briefly acting as chief of staff from 2 May to 10 June 1946. For his services in the Southwest Pacific and the
Occupation of Japan, Chamberlin was awarded three
Army Distinguished Service Medals and the
Silver Star. ==Later life==