phillies wrote:How would the rockets be different from explosive shells?
They wouldn't hit anything.
Are 50 calibre gatlings of some merit in warfare?
During WW2 Pacific there was a Marine Air unit, or so I am told, that took some number of aircraft used in ground attach roles and tested how many machine guns they could mount on one, with the aircraft still able to perform its mission. The answer was "lots". They were used to attack Japanese surface ships, freighters and on at least one occasion a destroyed, with or so I was told dramatic results. The incoming small rounds wiped out deck crew, folks manning the unarmored AA guns, bridge crew and bridge, and set lots of fires.
Against wooden ships and ships using sails, there is considerable merit.
You're talking about the Far East Strafer. It was originally a field modified B-25C with upwards of 12 50 cal machine guns firing forward it was later put into production as the B-25H(?). Some of the aircraft were also equipped with a 75mm howitzer. They also modified PBY Catalina's known as Black Cats with 6 50 cal the gunner actually sat on a saddle of asbestos over gun barrels to fire the guns. An example of how these planes fought read up on the battle of the Bismarck Sea.