Just a couple versions developed to allow the B-25 to contribute to the ground attack role. The bottom one is a B-25H which includes a 75mm cannon but it was manually loaded and found to have too low a rate of fire so was sometimes removed and replaced with 2 more .50 cal. The "J" model could have up to 18 .50 cals. A couple great examples of how versatile the B-25 could be.