AFAIK only the SSBNs are dual crewed, SSNs only have a single crew. The only country that dual crews SSNs is France I think.It is rarely talked about in mainstream media but the US Navy has very serious problems with crew fatigue, training, retention and the state of equipment. Almost all military blogs I follow that specialize on the US Navy mention this a lot. They get a lot of agreeing comments from former and current sailors too. Especially their surface force personnel spend 4-6 months every year deployed away from their families for no apparent reason. Ships do a lot of double deployments (two deployments without maintenance break in between) which wear down the equipment a lot. Their submarine force is fine though since they have 2 crews per submarine and don't conduct useless 6-month deployments without any maintenance breaks.
Really though what is the reason for the US Navy's global deployments?
Most USN deployments are a very long way from home base, hence the duration. Apart from Reagan, all CVNs are CONUS based.