Colt introduced the .38 Super cartridge in its Gov't Model in 1929.
The cartridge itself is a hotter version of the old .38 ACP round.
The rationale for this move was to attract law enforcement sales at the time. The .38 Super, in 1929, had a 130 grain bullet at 1300 fps. This round was good for penetrating the crude body armor of the 1920s, and it also did a number on car doors too. Remember, this was the age of bootleggers and frequent shoot-outs with automobiles involved.
Circa the early 1930s, the .38 Super was the hottest pistol round going. The .357 Magnum surpassed it in 1935. The .38 Super remained fairly popular in the U.S. until the 1950s. Meanwhile, it became very popular in foreign countries where private citizens cannot own firearms in military calibers. Colt chambered this round for many years in its 1911 variants. Lately, although not listed in its catalogue, Colt still occasionally makes pistols in .38 Super.
About five or six ammo manufacturers still load the round, although only Winchester's silvertip load and Corbon's hollowpoint round match the velocity of the 1930s specs. Today, it is comparable to a +P 9mm. For reloading, any bullet in the 9mm class can be used to load the .38 Super. I have heard that original bullet dimensions for the round were .357 or .358. Currently, it is .355: 9mm.
The .38 Super is a sweet shooter in the 1911 pistol. The round itself is highly under-rated and deserves more attention.
A series 80 Gov't model in .38 Super would a great pistol to own and shoot.