Thorn received a medal for hand-to-hand combat in which he captured a Confederate officer, an action that was personally witnessed by General Ulysses S. Grant.

Oscar Frederick Keydel, in Deeds of Valor: How America's Heroes Won the Medal of Honor (1901, pages 477 to 478), wrote: It was at the beginning of January, 1865.

To overcome these difficulties the resourceful Butler had caused a canal to be cut through the Dutch Gap peninsula, so that the enemy's batteries could be flanked and the obstructions in the river passed by the navy.

The main body of troops had been drawn off from the neighborhood of the vast mine for safety, and it was supposed that none had been left behind but the few whose duty it was to light the fuse and then escape.

The bravery of the officers before whose minds those thoughts flashed could not be doubted — it had been proved too often for that —but to go and warn the squad seemed so utterly beyond reason, so surely a useless throwing away of another life, that they stood there rigid and pale, with one exception - Walter Thorn, first lieutenant of the U. S. Colored Infantry, who hesitated, but only long enough to form a resolve.

Paying no heed, he ran on, reached the bulkhead, climbed to its summit, faced the storm of bullets that the rebels directed at him, and stood there until he had ordered the picket guard to flee to a place of safety.

He leaped from the top of the mine; the explosion took place; the earth was scattered in all directions and a great abyss remained, but the young lieutenant was unharmed.