The submarines will use a combat system by US defence company Lockheed Martin Corp and carry US-made torpedoes.
Admiral Huang Shu-kuang, Ms Tsai's security adviser, described the submarines as a "strategic deterrent" that could also help maintain the island's "lifeline" to the Pacific by keeping ports along Taiwan's eastern coast open.
China openly ridiculed Taiwanese hopes for what the submarines could do to defend the island.
“No matter how many weapons the Democratic Progressive Party buys, it will not obstruct the greater trend of reunification with the motherland,” said Senior Colonel Wu Qian, a spokesperson in China's Ministry of National Defense.
Have you picked up a history book? Taiwan literally still claims mainland China and the South China Sea as ROC territory. Maybe read Taiwan's Constitution instead of the American media interpretation of it? It's not my fault that you seem happier to spread ideology with American interpretations than deal with actual facts.