Is this really a "Key" book?
It was published 2 years after the first DC war book (OAAW 1) so it's not the first DC war book (far from it). It has no recurring characters. The title itself is the 4th or 5th most popular of the "Big Five" and carried the 5th or 6th most remembered continuous character (pair) when it did finally get continuity (Rock, HT, Dinos, Enemy Ace, then I think it's a push between Cloud, Pooch, and Gunner & Sarge) - and it wasn't even the title in which they premiered. There's no Kubert, no Heath.
Overstreet has an anachronistic tendency to always push the first issue of a title as a key and assign some arbitrary value to that, but in many cases it's not true. And I think this is one of them.