That was quite a versatile bird. I like the version with the multiple .50 caliber in the nose or the one with a 75mm gun that were used in the pacific. But my all time favorite of WW2 versatile bird is the De Havilland Mosquito which was used as a light bomber, recon and even as a fighter. It was also used to intercept V1 rockets.
The Mosquito was arguably the most effective aircraft in the entirety of WW2. Regarding the B-25, using the 75mm cannon created a lot of smoke in the forward area of the airplane. I'm not sure how effective it turned out to be in actual combat. Of course one shot from that cannon could sink a smaller boat, but the crew needed to vent the smoke after using. I'd imagine it was louder than heck as well having a cannon going off a few feet from where you're sitting.
Unfortunately I have never seen a Mosquito in person. Off the top of my head- WW2 aircraft I have seen in person and flying: B-29 B-25 B-17 B-24 Hawker Seafury(a bit of cheat since they were at the end of the war) Bearcat(same) Tigercat(same) P-51 P-47 P-38 P-40 Corsair Watching any of them fly is a treat- hearing them fly by is something else.
It was meant to be used against japanese fortification in place where the marines didn't have any artillery available beside "stove pipe" mortar and the target was only vulnerable from the front, like a cave entrance or a cliff.
A B-17 was at Spirit airport in St. Louis a few years ago. They wanted $400 to ride as a passenger for about a 15 - 20 minute flight. I told them at that price I wanted stick time...they said no can do for insurance reasons. So I only did the static display. I looked at the ball turret gun and thought...now there's the toughest job in the service...maybe only submariners could say they had it tougher. I had the privilege of flying (straight and level...nothing fancy) a C-47 (DC-3) years ago. One was a converted WW2 airplane at the time used for commercial cargo flying. I had some down time at an airport and was conversing with the crew. They said I could tag along on a short hop and then return to base. They let me "drive" the airplane once it reached altitude. A very stable old bird, input a little bit of trim and she held altitude and attitude quite nicely. Not a glamorous airplane like the B -17 or P-51, but a real workhorse in WW2.
Well since the Mosquito was made out of plywood, I don't think many would still be in flying condition...
Here's a few photos from the static display of a restored and flying B-17 taken at Spirit airport (St. Louis, MO) a few years ago. The view from the ball turret gunners station -