Over Germany, Italy, Japan, “Flak” (anti-aircraft gun) was, along with enemy fighters, the main threat to Allied bombers.
An Army Air Force training film explains FlaK (from the German word for Anti-aircraft gun – Flugabwehrkanone): how heavy, smal caliber and automatic gun worked, the way they could aim at aircraft formations flying at 27,000 feet and 320 mph and evasive maneuvers for bomber pilots to avoid being hit by anti-aircraft fire.
Obviously, technology behind AAA (Anti-Aircraft Artillery) has improved a lot since 1944 with radar guided bursts, but concepts like continuously pointed fire and predicted concentration are still used as a base of calculations required to shot down air intruders around the world; hence, even if you won’t face flak over Japan or Germany like U.S. pilots did 70 years ago, anti-aircraft artillery batteries still pose a threat to modern warplanes equipped with cutting edge EW (Electronic Warfare) suites and stealth planes.
H/T to Matt Fanning for the heads-up.