UK
The PIAT was Britain’s answer to the anti tank problem of WW2. Previous infantry anti tank weapons were scaled up rifles, which were large, heavy, and put enormous stress upon the user when firing. Not only that, but they were quickly becoming ineffective against modern armored threats. The answer was the PIAT. By firing a large HEAT warhead via a spring, as HEAT doesn’t need the projectile to be moving fast, or at all to penetrate, Britain’s infantry anti tank weapons were effective again.