S&W Hush puppies
I had the good fortune to be in at the beginning of the hi-cap 39->59. The seals wanted more rounds - not because they missed much, but because there were so many puppies to hush. I worked at the Naval Ordnance Lab, White Oak (Silver Spring, Md), 1961-1969. Best job I ever had.
I _think_ it was an NOL mechanical engineer named Shepherd who cut up a Browning High Power, took the grip frame, and attached it to a 39 that had had its grip frame amputated, did some heavy filing, and made a double row Smith that would feed. Some days. The first double row double action semi-auto, as far as I know. If it wasn't Shep himself, it was one of his machinists.
S&W was shown the gun, and told to make it work right. They did. I had nothing to do with it, other than drool on it. One of my best shooting buddies at the time got the job of writing the "Ordnance Publication" ("OP" = "TM" to non Navy types) on it. I resented him for years after that. I was stuck doing the dull books, on mines and missiles. Sigh.