Millin is most famous for being one of the few pipers to play during a World War II battle. Pipers had traditionally led Scottish troops into battle however the death toll among pipers in World War I was so high that the practice was banned by the British high command. Lord Lovat, however, ignored these orders and Millin, aged 21, played "Hielan' Laddie" and "The Road to the Isles" as his comrades fell around him on Sword Beach. As German soldiers later attested, they did not target Millin because they believed him to be mad.
This action was portrayed in the 1962 film The Longest Day. It is a common misconception that Millin played himself; the actor was in fact Pipe Major Leslie de Laspee, the official piper to the Queen Mother in 1961.