United States Army combat engineers were not properly trained to conduct their mission during World War II. Research of combat engineer training and operations during the interwar period and subsequently in the Pacific, North African, and European theaters revealed the extraordinary efforts required both to train new engineers and to develop selectees into capable combat engineer units. This research demonstrates that significant reductions to military personnel levels and readiness during the interwar period required a hasty fielding of forces in wartime that were not trained to previously established standards. Wartime engineer units consisted of soldiers who did not meet prerequisites for entry into the branch. These factors resulted in officers who were not prepared to lead combat engineer operations and soldiers who lacked basic engineering skills to efficiently conduct their missions. Shortfalls in selection and training often necessitated remedial training in the theaters of operation.