For centuries -- until about 30 years ago -- sailors tossed their trash overboard into the sea. Now Navy ships focus on protecting the environment as scientists at NAVSEA Carderock in Bethesda, Maryland, develop and evaluate ways to treat waste. Every ship is like a small city, with 100 to 5,000 people aboard. They produce refuse ranging from garbage to water waste, sewage to shower water and eventually must dispose of it all. Dishwater, for example, could pollute the ocean if it's dumped, so the scientists have created methods to treat it onboard so it can be safely discharged overboard. Plastics are another story -- they can never go over the side. Instead, they are compressed into large disks and returned to shore, where they may be recycled.