Refrigerator magnet pictures an illustration from a World War II advertisement promoting Martin's JRM Mars seaplane. The Martin JRM Mars was a cargo seaplane, or flying boat, built for the US Navy during World War II. It was the largest such vessel but only seven were built. It was used air sea rescue and anti-submarine warfare and transport. In addition to the Mars, Martin built 531 Boeing B-29 superfortresses and 1,585 B-26 Marauders, including the Enola Gay and Bockscar that carried the bombs to Hiroshima and Nagasaki.