Historicly, Dr. Gatling developed a motor driven gatling gun in the 1890's. It could fire 3000 rounds per minute, but wasn't developed.
Now, suppose that, in the early 1930's, the design was unearthed by the US Navy, and a 20 mm version is in service on some ships by December 7, 1941.
Japan also gets the technology, stolen from an American plant.
Pearl Harbor is still a catastrophy for the US Navy, of course...good weapons don't make up for surprise attacks, though the Japanese casualties might be heavier.
Does the battleship regain its prominence, since so many more planes get shot down? The 20 mm will get a lot of its victims as the aircraft are on the way out after dropping their loads...but a lot fewer planes from both sides will be making second strikes.
What else changes?
Now, suppose that, in the early 1930's, the design was unearthed by the US Navy, and a 20 mm version is in service on some ships by December 7, 1941.
Japan also gets the technology, stolen from an American plant.
Pearl Harbor is still a catastrophy for the US Navy, of course...good weapons don't make up for surprise attacks, though the Japanese casualties might be heavier.
Does the battleship regain its prominence, since so many more planes get shot down? The 20 mm will get a lot of its victims as the aircraft are on the way out after dropping their loads...but a lot fewer planes from both sides will be making second strikes.
What else changes?