Welliver was forced to depart the project because of a family health emergency, according to the site.
Executive-produced by Michael Bay, The Last Ship follows the crew of a naval destroyer who are among the only survivors on Earth after a global catastrophe decimates the world's population. Baldwin will play Mike Slattery, who is second in command to Captain Tom Chandler (recent Grey's grad Eric Dane). Tom and Mike, described as a fair man and a family man, occasionally clash.
Baldwin guest-starred on three episodes of Law & Order: SVU as Capt. Cragen's temporary replacement. Aside from his five-year stint on Chuck as growly spy John Casey, Baldwin is also known in the Whedonverse for his roles on Angel and Firefly.