phrase: refers to someone deceased in a military accident or operation. Phrase predates World War II, but came into common use at that time due to the large numbers of training casualties due inexperienced pilots/crewmembers trained in aircraft that are much less reliable than today. Common accidents in rural areas would result in aircraft crashing into barns, fields, or rural property, resulting in damages. The US Government would compensate the affected property owners with checks to pay for damages, or in some cases condemn land contaminated with undetonated/unlocated munitions/weapons, in effect "buying the farm".
"28 of us started out in my class in UPT (Undergraduate Pilot Training) but only 11 of us earned our wings. 13 washed out, 2 got held back, and Higgins and Baker bought the farm when they lost power on climb-out."