Taiwan

 Taiwan is a sizable country, with a lot of high tech industry, that is friendly to the United States.  It is an island, off the coast of China, and China thinks it ought to be part of China, under the control of the Chinese Communist party (CCP). Taiwan used to be part of China until 1947 when the communists took over China.  The Chinese nationalists, Chiang Kai-shek's party, retreated to Taiwan (Formosa it was called in those days).  China has wanted to regain control of Taiwan ever since 1947.  Only in the last few years has China become strong enough to make that a possibility.  

When Nixon and Kissinger did the opening to China back in the 1960's, one part of the deal that the Chinese insisted upon was for the United States to stop promising to defend Taiwan from Chinese attack. We have kept our promise to the Chinese on that subject.  Our state department called this policy "strategic ambiguity", we would not say we would  defend Taiwan but we would not say we would not defend Taiwan.  

The strait of Taiwan is 120 miles wide and deep enough to float aircraft carriers.  To defend Taiwan our navy has to move into the strait and sink all the landing craft loaded with Peoples Liberation Army soldiers.  The Chinese will use their navy to defend their troop ships and landing craft.  As of right now the Chinese have as many ships in their navy as we have in ours.  We need to build some more navy ships in order to have a bigger navy than China does.  

Biden just came right out and said we would defend Taiwan, which is the right thing to say, we need Taiwan.  To back up those words we need a navy strong enough to prevent the Chinese from landing troops on Taiwan.