US Navy aircraft carrier weight gain problem

One of the examples, referenced in the paper "Materials for the 21st Century," is a study done by the US Navy. Aircraft carriers gain about 250 tons a year. If you look at the last 50 years, you take the Nimitz-class carrier — they built a new carrier every one or two years, so we've had twenty-some carriers since the Nimitz, all the way up to a new whole class now. The Nimitz hull design went for about 50 years, and if you look at the weight of the Nimitz, which is in the 60,000-ton class, to whatever the last carriers were, which are up to about one and a half times that, the average weight gain on an aircraft carrier was 250 tons a year. Most of it unfortunately is up in the superstructure or near the top deck, instead of the aircraft deck, and that's a problem for stability. So the Navy was looking at going to a higher-strength steel for the hull. They were going to go to an HSLA 60, and they wanted to know what the cost savings might be.