Lieutenant Donald W. Johnson, pilot of the 339th Fighter Group, watches on as Captain Charles D. Nethaway demonstrates how the "G-suit" worked. "G-suits" were developed to counter the blackouts that pilots suffered when the G-force on their bodies during tight turns forced the blood from their brain to the lower part of their body. Inflated by the exhaust of the P-51 Mustang's vacuum system, the suits applied pressure to the pilot's legs and abdomen, forcing the blood to continue to circulate around the upper body. The suits were issued to 339th Fighter Group in June 1944.