TAIPEI, Taiwan — China's navy has commissioned a new-generation frigate as competition rises with the U.S. and other regional powers, saying the ship will “play a vital role in enhancing the overall combat effectiveness" of its forces. China already has the world's largest navy in terms of number of hulls, although its technology is sometimes seen as lagging. Its largest competitor, the U.S., has warned its Navy could be outnumbered and has called for a building program as well as reforms to