The artillery he directed killed German infantry. The machine gun fire he directed from the M10 hit German infantry at close range. The combined effect disrupted the German advance sufficiently that the German infantry withdrew, and without infantry support the German armor also withdrew. Company B’s position was not overrun.
The specific contribution of each element to this outcome cannot be precisely allocated. The artillery was doing damage before Murphy climbed onto the M10. The M10’s machine gun added to the defensive fire. The withdrawal of the German infantry was a decision made by German commanders in response to conditions that Murphy’s actions contributed to but did not entirely create. The counterattack restored the company’s forward positions.
What can be said specifically is that Murphy’s presence and his actions — staying when his men withdrew, calling in fire when both M10s were disabled, climbing onto the burning vehicle, firing until the ammunition was gone — were the central documented features of a defensive action that held the company’s position against a larger attacking force. The citation’s credit of approximately fifty German soldiers killed or wounded through the combined artillery and machine gun fire is the official account, not an independently verified modern count.
The question of why he did it has the answer he gave: “They were killing my friends.” The answer is not a tactical analysis or a calculation of probabilities. It is the simplest explanation available, offered by the person who was there, in a situation where the people he had served with for three years were being killed and he had a burning tank destroyer in front of him with its machine gun pointed at the people doing the killing.