What the Springfield 1903 could have been, might have been, but never became.
The Pedersen Device turned the bolt-action Springfield 1903 into a semi-auto firearm. This was top-secrect stuff back in 1917.
“It began in the late summer of 1917 when Mr. John D. Pedersen … walked into Ordance chief Crozier’s office and offered him the chance to see something truly amazing. … Producing a Springfield, Pedersen squeezed off a few shots in the regular manner, and then (in the words of Major Hatcher, an ordnance expert) ‘suddenly jerked the bolt out of the rifle’ and quickly replaced it with a ‘mysterious looking’ mechanism. As observers exchanged wondering glances, ‘he snapped into place a long black magazine containing 40 small pistol cartridges.’ … Each cartridge, they found, was of the same caliber as the Springfield’s standard ammunition but one-fifth the size.”–Alexander Rose, in the chapter “The Paths Not Taken,” from his book American Rifle, A Biography