Harrod is the commando team's radio man on the mission to rescue General Carnaby, who is being held in the German castle known as the Schoss Adler. Sadly, he isn't around very long.
Immediately after the team parachutes into Germany, it is noticed he is absent. Smith goes looking for him and discovers him nearby in the snow with his neck broken. We're left to wonder, did the fall kill him, or, perhaps more sinisterly, is there a traitor in their midst?
It is later revealed that it's most likely the latter, as in addition to rescuing Carnaby, Smith's mission is to uncover the identity of some Nazi spies. Harrod was one of the suspects, which is why he was chosen for the mission. Harrod is thus proven innocent... but unfortunately for him only because one of the real traitors killed him.
With nothing further that he can do for poor Harrod, Smith merely appropriates the radio, reports his death to the others. In order to prevent the remaining four suspected traitors from thinking he's on to them, Smith explains he thinks Harrod broke his neck in a bad landing. They press on.
He isn't killed onscreen and the film never confirms which of the traitors did him in.