OK from one who lived through it. The Korean and Vietnam Wars were giving the military a bad name and sales of GI Joe, the military figures were tanking hard. Hasbro dropped the direct military approach and created the Adventure Team. The AT still wore dog tags, still had military ranks, still used a LOT of military gear but were sent on 'adventure' missions to hunt down exotic animals and lost cities rather than combat. And yes back in the day all GI Joe figures were the same with different hair color and clothes, same as Barbie and any other 12" figures of the time. Evan the first 2-3 years of Big Jim was a single head sculpt with new hair color to create the 3 main characters.
The helicopter, sub and 6-wheel tank are all updates of vehicles sold in the 12" line in the early 70s, I had all three. and NEED these for that reason only.
Choose the things to fill your mind or the world will fill it for you.