The M-4 75mm cannon was a significant modification that transformed the B-25 G/H Mitchell into a formidable "flying field gun." This large cannon was adapted from the M-4 tank gun, which was typically mounted on the ground or on tanks. To accommodate this powerful weapon within the B-25 G/H, the aircraft's interior had to be substantially modified.

Key Modifications for the M-4 75mm Cannon:

• Installation Location: The cannon was mounted in the nose of the aircraft, specifically in the space that had previously served as a crawl-way for the bombardier. This area had to be reconfigured to hold the weight and bulk of the cannon.
• Mounting Structure: The M-4 cannon and its carriage assembly were securely bolted to the floor of the aircraft. A flatbed of steel was constructed to provide a stable and reinforced base for the cannon, ensuring that the recoil from firing would not damage the aircraft's structure.