The greatest unsolved mystery about World War II is what else television could possibly have to say about it. From the old CBS documentary series The Twentieth Century (11 of the 18 episodes of the inaugural 1957-58 season were devoted to the conflict) to Ken Burns' 14-hour 2007 opus The War, it sometimes seems that every bullet fired has had its 15 minutes of fame.
Yet nearly every afternoon, you can find the History Channel or the National Geographic Channel or one of their rivals exploring new nooks and crannies.
The latest entry in this marathon, television critic Glenn Garvin notes, is Bombing Hitler's Supergun, an episode of the PBS documentary series Nova. It's a brisk recounting of Hitler's attempt to build a cannon that could hit London from France, one of many superweapons conceived in a final desperate attempt to stave the end game in the grim final days of World War II.