I've found an even earlier reference to them - 1928 -
here about half way down the page (turn your sound off before clicking the link
)
I've pasted the text so you can avoid the annoying music.
When Air Chief General Hap Arnold called George Kenney to Washington, D.C., in the spring of 1942 to ask him to transfer to Australia and fix the mess that was the Far East Air Force, Kenney made two special requests. One was for fifty P-38 fighter aircraft and pilots (including Lieutenant Bong) to fly them. The other was for a shipment of 3,000 parachute-fragmentation bombs. Kenney advised Arnold that if he was to assume command of the Pacific air operations, he wanted total air superiority--"air control so supreme that the birds have to wear Air Force insignia." This could only be achieved by the destruction of Japanese airplanes, either in the air or on the ground. The P-38s would knock them out of the air, the para-frag bombs would destroy them before they ever became airborne.
Para-frags were small small, ten-kilogram (23-pound), explosives that could be hand-thrown from aircraft to slowly descend to earth and explode on impact. They could be very quickly scattered across a wide area from a low-flying B-25 Mitchell or A-10 Boston, and would settle into the smallest opening behind the revetments enemy engineers had created to protect their planes while on the ground. Upon detonation they spewed out nearly 2,000 shards of white-hot metal to tear through wings and fuselages, rupture gas tanks and to set grounded planes on fire.
Five thousand of these para-frags had originally been manufactured in 1928 for shipment to Australia, but only 2,000 had been delivered. The 3,000 requested by General Kenney was the remainder of a weapon stockpile that more than a decade later, no one else seemed interested in. Ken's Men put them go great use with their innovative minds, coupled with the creative genius of an aircraft engineer the men of the Fifth Air Force called "Pappy."