An interesting article (with short video) on how a piece of military gear—in this case, an individual first-aid pack—is designed at the Natick Soldier Systems Center. (I think that Natick also designed the Polartec-insulated Generation III Extreme Cold Weather System clothing for the military.)
In the video, the designer speaks of starting with "an existing SAW gunner pouch" for the first version of the first-aid kit.
Ah, that's where the individual fire shelter pouch came from too! It sure fits the definition of "just kind of a brick on your side that gets in the way of everything." If you were issued the Large model, it's too big for the quick-extraction pocket on many fire packs.