He died, aged 31, on 16 September 1943 from wounds received in action while leading a group of Commandos. He is buried in the British Salerno War Cemetery, Bivio Pratole in the province of Salerno, Italy.
At the time of his death he was a Captain in command of a Troop in No 2 Commando, commanded by LtCol 'Mad' Jack Churchill, who was not related to Winston Churchill despite some media statements to the contrary.
Both No 2 and No 41 Commando Royal Marines were engaged at Salerno, both switched from their initial battle area around Vietri sul Mare, west of Salerno, to a position two to three miles inland of Mercatello, then south east of Salerno, today it is an encompassed suburb. The Germans held and were strengthening three high-ground positions. During the daytime of 16 September, No 2 Commando moved back though a valley around the village of Piegolelle dubbed 'Pigoletti', which had been cleared the night before, intending to capture a hill at the far end referred to as 'Pimple Hill'. However, in the early hours the Germans had sent light forces back into the valley and also strengthened 'Pimple Hill'. On assaulting the hill two troops of commandos were exposed to well-positioned machinegun fire. The Duke was among the fatalities, hit by a sustained burst from a Spandau position.
The Salerno War Cemetery is one of a hundred and twenty Commonwealth cemeteries in Italy.