Reviewing the lessons of World War II, Lt. Gen. Leslie R. Groves declared: "Mobilization was decisive and construction generally controlled mobilization." In 1939, when hostilities began in Europe, the United States was ill prepared to counter threats to its security. To be sure, the Navy, the first line of defense, ranked with Britain's mighty fleet. But the Army was barely more than a token force, and the country had virtually no munitions industry. Before the nation could realize its huge military potential, it had first to build a vast complex of camps, plants, airfields, hospitals, and depots. As Presidential adviser Sidney Hillman pointed out in 1941:
Construction is not only the biggest single part of defense, it is also the first step in defense. Before we can produce guns and planes and tanks, we must build defense plants or alter non-defense plants to new production . . . . Similarly, if we are to train our Army well, our soldiers must be provided with proper living conditions in camps and cantonments.