On that day, near Cassino, Italy, Riordan single-handedly silenced a German machine gun emplacement.
Second Lieutenant Riordan's official Medal of Honor citation reads: For conspicuous gallantry and intrepidity above and beyond the call of duty.
In the face of intense fire, 2d Lt. Riordan moved out in full view of the enemy gunners to reach a position from where he could throw a handgrenade into the pillbox.
Continuing the assault into Cassino itself on February 8, 1944, 2d Lt. Riordan and his platoon were given the mission of taking the city jail house, one of the enemy's several strongpoints.
2d Lt. Riordan's bravery and extraordinary heroism in the face of almost certain death were an inspiration to his men and exemplify the highest traditions of the U.S. Armed Forces.