The M115 was a 500-pound (227 kg) bomb that was converted from a leaflet bomb and to be used to deliver wheat stem rust. Wheat stem rust culture consisted of a dry particulate matter which was adhered to a light-weight vector, usually feathers. Because of its method of dissemination, the bomb was commonly referred to as the "feather bomb". The feathers would fall over a wide area when released. The M115 was shown to establish 100,000 foci of infection over a 50-square-mile (130 km2) area.
According to a 1950 military report the M115 was tested in an area 11 miles (18 km) long and 1.5 miles (2.4 km) wide. The area consisted of 7.5 acres (30,000 m2) plots sown with the Overland variety of oats, susceptible to the test agent, Puccinia graminis avenae, but not to other strains of cereal rust. The test drops of the M115 showed that, from an altitude of 4,000 feet (1,200 m), feathers could be spread over an area of 12 square miles (31 km2). Three M115 feather bombs were dropped 1 mile (1.6 km) upwind from the target area, which was then monitored for any changes. Estimates showed about a 30% reduction in yield from the infected area.