Following the outbreak of the Second World War, Hunt volunteered as a sapper waterman in the Royal Engineers, and served in the Battles of Narvik – part of the Norwegian campaign) – in April–May 1940. By 1944, he was commissioned, and as a captain commanded fifteen of the Rhino ferries on Gold Beach on D-Day. In four months, all sixty-four of these landing craft put ashore 93,000 units (tanks, guns and vehicles) and 440,000 tons of military stores. During the last six months of the war in Europe, together with the Dutch hydraulics engineer Lt. C. L. M. Lambrechtsen van Ritthem, he advised the Chief Engineer Second Army, Brigadier "Ginger" Campbell, on the "opposed crossing of water obstacles", so that the longest floating Bailey bridge of the Second World War could be constructed at Gennep in the Netherlands. This bridge over the river Maas (Meuse) was long, and was opened on 19 February 1945.