This is an early Gerry rucksack. As I’ve probably mentioned in other posts, the earliest outdoor gear was simply repurposed military surplus and this bag shares many characteristics. Beyond the olive drab nylon the bag resembles very much a European military pack. Specifically one from a company called Bergans of Norway , which was made of more traditional materials, canvas and leather.
Though the design itself may not have been revolutionary or visionary the removable lightweight back panel is. I believe the panel to be made of fiberglass, but may just be something similar. The removable panel replaces metal support systems used on earlier packs. The updated support system with the use of lightweight nylon saved this traditional design many extra pounds.