The effectiveness of the German and United States submarine campaigns during World War II is compared by analyzing the genesis of each campaign, the commitment to each and the effort to overcome the losses imposed by submarine warfare. This comparison highlights one aspect of the strategic and operational consequences of conflict with an adversary able to build and maintain a superior industrial base in support of the military effort. This analysis places primary focus on German U-boat efforts in the Battle of the Atlantic and the U.S. submarine efforts in the Western Pacific. Ultimately, the overriding factor in the outcomes of both campaigns was the ability of the United States to produce more ships than the Germans could sink, to build more submarines than the Japanese could sink, and to sink more Japanese ships than the Japanese could build. As a result, the United States was able to sustain its' total military effort against Germany; Japan was not able to sustain its efforts in the Pacific. With the present U.S. requirement for trans-oceanic logistics for force projection, the lessons of WWII should remind us not to downplay the threat of adversarial submarines or to continue to lose the ability to muster a credible shipbuilding industry in the event of mobilization.Before commencing a military operation, War College doctrine advises review of four basic questions. First, what military condition must be produced in the theater of war or operations to achieve the strategic goal; Second, what sequence of actions is most likely to achieve that condition; Third, how should the resources of the force be applied to accomplish that sequence of actions and; finally, what is the likely cost or risk to the joint force in performing that sequence of operations. Both Germany and Japan needed to ask these questions as they sought to expand their empires through regional conflicts prior to United States' entry into World War II. Both recognized the criticality of sea lines of communications to achieve their strategic goals - Germany to defeat Britain and Japan to sustain its' own war effort and economy. Both also recognized the risks of provoking the United States into entering the war against them, yet both, when war with the United States did occur, had done little to overcome those risks. Once the United States entered the war, neither Germany of Japan could counter the U.S. industrial might economically or through direct or indirect military efforts. The submarine campaign that the United States carried out in the Pacific against Japan was instrumental in bringing Japan to defeat. Germany's U-boat campaign in the Atlantic against U.S. and Allied shipping was thwarted. Numerous reasons, including leadership, tactics, and technology have all been cited as causes of respective success and failure. These are all valid. Ultimately, however, both campaigns came down to wars of attrition. When the final counts are analyzed, the U.S. simply built more merchant ships than the German U-boats could sink; U.S. submarines sank more merchant ships than the Japanese could build and built more submarines than the Japanese could sink.