Caretaker of the injured or medic, Harden was a part of the British Royal Army Medical Corps. On 23 January 1945, he was in his unit's command post near the bridge crossing the Vlootbeek when news reached him that a group of the British Marine Corps' commandos had come under heavy German machine gun fire nearby. They had immediately taken cover, but that did not apply to three seriously injured men whom they had to leave behind in the snow. Under the rattle of enemy fire, Harden crawled to the wounded through open terrain for at least 150 meters. Although it was visible that he was a medic, the German soldiers continued to shoot. Nevertheless, Harden managed to reach the three victims and provide first aid.

After reporting to the command post, he crawled back for wounded men again. One of them, Marine Wheeler, had a serious leg wound and was lying near a spot where some cover was still possible. When the German soldiers realised whom Harden was heading toward, they concentrated their fire. After making it to Wheeler, Harden took the wounded man on his shoulders and carried him to safety, while zigzagging through the open field. Although Harden got injured in the rescue operation, he immediately turned back to pick up the two others. Some tried to convince him that it was wiser to wait for tanks to arrive. But Harden did not allow himself to be persuaded. He knew the condition of the wounded and understood every minute counted. He gestured for help. Two Marines left cover and joined him. They crawled after Harden with a stretcher. They reached the heavily bleeding Marine Wales without any harm. After they put him on the stretcher and starting their retreat, the German machine gun fire intensified. The injured Wales was hit again and died from his injuries moments later. 

The third and final trip through the open field ended fatally for Harden. Once again, he set off with the two volunteers. The third wounded man, Lieutenant Corey, was already dying when they reached him. They were almost safe when a bullet hit Harden in the head. He died instantly.

The British general who spoke at the posthumous presentation of the decoration said verbatim: “I do not remember ever reading anything more heroic.”