In January 1945, the Sixth Army embarked on its largest, longest and last campaign, the invasion of Luzon. Krueger intended to make "maximum utilization of America's materiel and industrial superiority".[72] Once again, intelligence estimates of Japanese strength were questionable. MacArthur's intelligence officer, Brigadier General Charles A. Willoughby, basing his estimates on Ultra, believed that there were about 172,000 Japanese troops on Luzon.