I crossed the Pacific six times between 1951 and 1961 on MSTS. Seattle to Yokohama. Yokohama to Seattle. Not exactly a cruise line, tho.
About 30 years ago I took two Mediterranean cruises free of charge. Unfortunately it was aboard the USS Nimitz and the accommodations were sub par. Was able to visit some interesting places though.
You were there to work. And you didn’t pay big bucks for all those sailings. :)