People tend to think of quick-detach slings as the stuff of nylon and fast-ex buckles, but these things have actually been around for a long time. One example is this Japanese Arisaka sling. Using two wire clips to attach to sling swivels, it is very quick and easy to detach from the rifle. We don't know exactly who these were intended for, but they ended up being used on a wide variety of rifles. In particular, they appear to have been fairly popular on the Type 2 Paratrooper model of the Arisaka - although they were made before that rifle was adopted.