One US carrier is always in the vicinity of Japan and the Korean peninsula. I haven't kept up, but I'm sure Tokyo Bay and Yokosuka are still open to US ships and planes.
Nimitz Class:
USS Nimitz (CVN 68) - San Diego, CA
USS Dwight D. Eisenhower (CVN 69) - Newport News, VA
USS Carl Vinson (CVN 70) - Bremerton, WA
USS Theodore Roosevelt (CVN 71) - Norfolk, VA
USS Abraham Lincoln (CVN 72) - Everett, WA
USS George Washington (CVN 73) - Norfolk, VA
USS John C. Stennis (CVN 74) - San Diego, CA
USS Harry S. Truman (CVN 75) - Norfolk, VA
USS Ronald Reagan (CVN 76) - San Diego, CA
Nuclear-powered Nimitz-class aircraft carriers are the largest warships in the world. Each ship was built by the Newport News Shipbuilding Company with commission dates spanning from 1975 to 1998.
Length: 1,040 feet
Flight Deck Width: 252 feet
Beam: 134 feet
Displacement: approx. 97,000 tons full load
Speed: 30+ knots
Aircraft: approx. 80, depending on type