(or "What Makes A 'Cult Classic'?")
'Enemy Ace' was published (as a back-up in 'Star-Spangled War Stories', 'Men of War', and 'The Unknown Soldier') during the last great flowering of war comics from DC. It was an era in which the genre did amazingly well, breeding long-running, famous, enduring characters like Sergeant Rock, The Unknown Soldier, and The Haunted Tank (just to name a few.) 'Enemy Ace' came along towards the end, in the mid-to-late 1970s when superheroes were beginning to truly dominate the medium, and it had the kind of storytelling engine that lends itself well to creating a "cult classic" series.
The key word, of course, was "Enemy". 'Enemy Ace' told the story of a German pilot, Hans von Hammer, also known as "The Hammer of Hell". The storytelling engine completely inverted the normal setting for war comics by taking the point of view of an enemy soldier, and using World War I instead of World War II (which had been the setting for most war comics of the era; the Nazis made perfect villains, and the conflict lent itself well to heroic narrative.)
The result is something unlike any other war comic of its era, and indeed like very few war stories at all (with the possible exception of 'All Quiet on the Western Front'.) War is portrayed as merciless and capricious, a killer of the just and unjust alike regardless of which side you're on. von Hammer's frequent catch-phrase, "The sky is the killer of us all," suggests that the pilots of both sides have more in common than they do in opposition, even as they attempt to murder each other. (The stories frequently play up the supposed chivalry of pilots in WWI; one story revolves around von Hammer inadvertently shooting down a plane whose guns had jammed, and his personal attempt to atone for the dishonorable action.)
von Hammer himself is like no other war character; he's not a leader of men like Rock or Jeb Stuart. In fact, his own men feel uncomfortable around the pilot they call "a human killing machine"; the only real supporting cast is von Hammer's orderly and the black wolf he finds in the German forests (which Garth Ennis famously suggested was a figment of his imagination.) He's aloof, fatalistic, and melancholy, traits you don't generally see in a comic book hero.
All of these are, of course, characteristics that don't necessarily translate well to long life for a storytelling engine. It's not really calculated to have the same appeal as your Sergeant Rocks or your Nick Furies. And yet, those very things that seem to doom it actually help it in the long run. Because 'Enemy Ace' is so different from other war comics, it stands out clearly in the memory of even the most casual reader. This is not like anything else in the genre, and nobody can pick up a story of 'Enemy Ace' without being struck by how unusual it is. It haunts the reader.
That's where a cult classic begins. It begins by going against the grain, by striking the reader with a glimpse into a strange and unusual world that they've never seen before. It sticks in the memory the way a more mainstream engine doesn't. And so the reader remembers it, and discusses it, and passes the knowledge of it on like a secret they're willing to share with people they think are capable of "getting it". And so, down the years, the reputation of 'Enemy Ace' only grows, despite the relatively few stories Bob Kanigher and Joe Kubert did with the character. It's genuinely unique, and although a lot of people fear the strange and unusual, more than a few people are attracted to it.