Even though the United States did not enter World War II until the attack on Pearl Harbor in December of 1941, it had been preparing for the likely possibility of joining the conflict for some time. Naval forces around the Pacific had been actively operating drills and exercises to stay sharp and prepare as tensions with Japan increased. As the Japanese Empire expanded closer to the Philippines, President Franklin Roosevelt issued a national emergency declaration that gave him significant authority to oversee military and civilian coordination.
As late as 1940, Roosevelt had been corresponding frequently with British Prime Minister Winston Churchill about contingencies should the United States join the conflict. Although he assured the nation that he planned to keep the United States neutral, privately he wanted to join the fight against fascism. The two leaders frequently discussed how the countries would assist each other in the war. In fact, diplomatic missions between the United States and Great Britain, the Soviet Union, and China increased significantly during this time.
Roosevelt also bolstered the Office of Naval Intelligence in its efforts to gather information through clandestine operations around the globe. US intelligence officers were stationed in many countries involved in the war to gather as much useful information as possible.
Aware that the United States might become a target as a result of its support of Allied forces, coastal defenses were built up around major American ports. The country also instituted a draft in 1940 to shore up its defense forces: the only peacetime draft in the country's history. The pre-war period was also marked by increased military recruiting.
Furthermore, the manufacturing of supplies and equipment vital to the war effort was ramped up, particularly the production of munitions, tanks, military trucks, and warplanes. In fact, after the fall of France in 1940, Roosevelt asked Congress for one billion dollars to be used in warplane manufacturing.
Roosevelt also reconvened the National Defense Advisory Commission (NDAC). This body of industry leaders and public consumers was first created during World War I. It served to advise the government and act alongside it to implement private sector efforts to prepare for war. In January of 1941, the president replaced the relatively toothless NDAC with the Office of Production Management (OPM). This body was charged with encouraging industrial production to aid a potential war effort.