To be honest subs are one of the things I always see reason in building. They are the ultimate weapon of war today and for a superpower like the US, Russia or China they should be the emphasise of the defense industry. Aircraft carriers are weapons of imperialism and enforcing your policies on other countries across the globe, nuclear submarines with their arsenal of weapons of mass destruction can't be used for such purposes, but they are a good deterrent against war on your own country.

With the Russian Typhoon class submarines still at the pinnacle of submarine technology(in most areas) and the Project 955 submarines entering service it's understandable if the Americans don't want to be left behind. That and also the Virginia class is expected to serve for the next 5 decades or so. Sounds more like a reasonable long term investment to me.