As the strategic bombing campaign over Germany built up in the spring of 1943, losses over the skies of the Reich began to mount as mission momentum increased over the course of that summer. While the ever-present flak was a significant threat to the B-17 Flying Fortresses and B-24 Liberators of the US Eighth Air Force based in the UK, it was the fighters of the Luftwaffe that were mauling the formations. From June into the autumn, losses were mounting and doubts were starting to be raised on the operational wisdom of daylight strategic bombing. The breaking point came on 14 October 1943 with the second attack on the ball-bearing plants at Schweinfurt, Germany. Already bruised from a vicious mauling at the hands of the Luftwaffe on the first raid on the Scweinfurt (which was attacked along with Regensburg on 17 August 1943 with the loss of 60 bombers), of the 291 B-17s sent on the mission, 77 bombers were lost and 122 were damaged. The day was named "Black Thursday" for having the highest number of crewmen lost on a single USAAF mission- 590 killed, 65 taken prisoner. Deep penetration missions of Germany were suspended until February 1944 when the long-range P-51 Mustangs arrived.
But warnings were raised as early as 1942 stateside when Major Cameron Fairchild of the USAAF sought ways to improve the aerial gunnery skills of the men who manned the defensive positions on the heavy bombers. The techniques of training at the time were fairly basic, ranging from skeet shooting to firing at towed targets. Fairchild surmised the best aerial gunnery training would consist of being able to fire live ammunition at an actual fighter aircraft. His first task was to develop a bullet that had the same characteristics as a 30- or 50-caliber round but would splinter harmlessly on impact. Working with researchers at Duke University, the University of Michigan, and the Bakelite Corporation (one of the pioneering manufacturers of plastics), Fairchild and his team came up with a frangible bullet that was weighted with powdered lead to give it the proper weight and density.
Fairchild proved to be willing to circumvent the usual Army bureaucracy to promote his ideas. Instead of working through the usual Army weapons development channels, he teamed up with academics to validate his ideas. Fortunately, the heavy losses of 1943 showed that aerial gunnery skills were lacking and Fairchild's frangible training bullets gained traction with the USAAF. He then selected the Bell P-63 Kingcobra as the target aircraft. As it was a type not used by front-line USAAF units, it was easily available. The P-63, designated RP-63, was given 1-inch thick armored glass with special armor in vulnerable areas. Sensors underneath the RP-63 registered hits and lights on the spinner and on the fuselage would light up, giving rise to the name "Pinball".
Beginning in early 1945 RP-63 Pinballs would fly attack profiles against bombers with student gunners before they were assigned to a combat unit. A training B-17 might have 12 student gunners each having 2,000 rounds of Fairchild's special frangible ammunition to fire at the Pinballs. The Pinball pilots, flying RP-63s that were painted either dayglo orange or yellow, flew 2-3 missions a day from bases throughout the United States. Minor damage was easily repaired on the flightline but the Achilles heel of the Pinball was the wingroot air ducts that provided cooling air to the mid-fuselage mounted Allison V-1710 liquid-cooled engine. If a frangible bullet got into the duct, the fragments could damage the cooling system, resulting in an overheating engine and a mandatory deadstick landing or a bailout by the RP-63 pilot.
A total of 300 P-63s were converted to the RP-63 Pinball configuration. Some aircraft also trained B-29 Superfortress gunners, but by 1947, the Pinball program was wound down and the last aircraft retired. Much of the early demise of the program came with the introduction of the centralized gunner control system in the Boeing B-29 Superfortress where analog systems provided the necessary lead and tracking for the gunners which used sights that remotely operated the turrets. Targets could be handed off from one gunner's sight to another and it made aerial gunnery training obsolete. The second factor in the demise of the Pinball program came with the gun-laying radar that was first introduced on the tail cannons of the Convair B-36 Peacemaker. Radar simplified tracking and accurately shooting at target aircraft. But the Pinball program lives on as an unique wartime solution that undoubtedly did its part to hasten the demise of the Axis in the Second World War.
Source: Air & Space Smithsonian, November 2010, Vol. 25, No. 5. "Just Shoot Me: In World War II, P-63 pilots had to learn to take it- and not take it personally" by James Dunaway, p50-53. RP-63 model by Scott Van Aken.