Against the thick armor of North Korea's T-34 tanks these were not much of a match, but they tried.
In the Korean War, these lower caliber anti-tank guns were most effective against infantry where unsupported by armor.
The Communists used 45mm anti tank guns with murderous effect against attacking infantry. The NK, in particular, deployed them against the Fifth Marines when we re-captured Seoul after Inchon. Surviving Marines still recall those deadly red fireballs.
Causes of the Korean Tragedy ... Failure of Leadership, Intelligence and Preparation
The Foundations of Freedom are the Courage of Ordinary People and Quality of our Arms