In January 2012, President Obama announced America's shift in strategic focus to the Asia-Pacific region. While the administration seeks enhancement of America's relationship with China to secure vital U.S. economic and security interests, the lack of transparency in the build-up of the Chinese submarine force may threaten this goal. Advancements in the numbers and capabilities of China's diesel-electric submarine fleet are enabling development of its area denial capability in the vast littoral areas of the Western Pacific. Improvements in China's nuclear fast-attack submarine force are expanding the nation's reach and regional focus to an increasingly large expanse of the Pacific while helping to turn China's navy into one of the world's most formidable blue water forces. Planned reductions in the U.S. submarine force end-strength threaten to shift the balance of naval power in the Western Pacific to China. A comparative analysis of the U.S. and Chinese submarine fleets provides key insights regarding the Department of Defense imperative of meeting the nation's operational demands in the Western Pacific.