In 1900, JM Browing designed the .38 ACP, a semi-rimmed round (meaning the case rim stuck out just a little wider than the case body) using a case 0.90" long, and firing a 130gr fmj bullet at approximately 1050fps.
In 1902, S&W introduced the .38 Special, a straight walled rimmed round using a case 1.19" long, and firing a 158gr (lead) bullet at approx. 850fps.
In 1929, the .38 ACP was "upgraded" with an increased pressure loading, becoming the .38 Super. The new load used the same case and bullet, but fired at approx. 1,300fps. The new load was too hot for the older .38ACP guns. Today, all the .38 Super ammo I see is marked .38 Super +p
.38 Super and .38 Special ARE NOT THE SAME THING!
Folk-lore has it that it was developed to counter bullet-proof vests said to be worn by gangsters in the Prohibition Era.
That is quite possible, but from what I've read that would have been an added benefit. What the bigger concern was, was cars. The "motor bandits" of the Prohibition era were often in cars, cars with, by todays standards, THICK metal bodies. The .45acp (even out of tommyguns) gave notoriously poor penetration on those car bodies. (or was seriously "out of gas" after getting through the car body). The .38 Special, with its relatively soft lead bullet was also far from ideal. Special "metal piercing" ammo was made for both, but usually wasn't where it was needed when it was needed.
Nobody American was using the 9mm Luger in those days, and in fact virtually all the 9mms in the country were Lugers, in those days, and 9mm performance wasn't what it is today, either. A 124gr FMJ @ 1050fps or a 115gr FMJ @ 1150fps.
A 130gr @ 1300 from a .38 Super was a serious increase in punch.
Until 1935, when S&W came out with the .357 Magnum.
After that, the .38 Super just kind of faded out, though it never died, it was not a popular round in the US for a long time. It was, however a very popular round south of the border. Very popular in Mexico and many other latin American and South American countries were there were laws against owning "military" calibers.
Hope this helps end your confusion.