OAAW #218 is technically bronze age, but the backup story is the first appearance of the USS Stevens series, which became a storied, long running back up feature in DC's war books. Generally considered a key.
OAAW #196 is a very important book, in that it marks the beginning of Joe Kubert's editorial run on the title (and the other DC war books). But what's critical is the shift in tone that this book represents... Kubert made a distinct editorial decision to use the war books as an antiwwar statement in response to Viet Nam, starting with OAAW 196. He wanted to portray the characters less as superheroes and more as just humans with strengths and weaknesses, flaws and virtues. In this issue, Sgt. Rock basically has a breakdown in response to the unending combat. He's portrayed as vulnerable and painfully human, and he questions everything. I had a chance to speak to Joe about this many years ago, and I asked him point blank if it was overtly his intention to make an antiwar statement through his editorship, and indeed he said it was. In many ways, an strong argument can be made that this actually the first book of the bronze age, depending on how you define that era. If we see the BA as a period where the stories are more mature, more reflective of the culture, where the focus on characters turns more towards their humanity rather than just their superpowers, this is the book that started that... all by Kubert's design.
Argument can also be made that OAAW #160 marks the beginning of this approach. But #196 seems to mark the real shift in gears that propels this title in the storytelling style of the bronze age.
Shep