Today in History, January 5, 1943:
The light cruiser USS Helena is the first to utilize an anti-aircraft shell equipped with the newly invented radio proximity fuse to shoot down a Japanese dive bomber attacking American ships.
Prior to this anti-aircraft fire had been somewhat inaccurate. The proximity fuse used radio waves projected from the fuse to detonate the shell when it came within range of the enemy aircraft.
Now gunners only had to get their ammunition aimed toward the enemy aircraft, getting the range didn’t matter. The invention is credited with shortening WWII by a year and saving countless lives as a result.