RAF Hell's Mouth was a World War II Royal Air Force grass airfield at Hell's Mouth, (Porth Neigwl) on the Llŷn Peninsula near Abersoch, Gwynedd. RAF Hell's Mouth was commissioned in February 1937 as a Relief Landing Ground, later an Emergency landing Ground for RAF Penrhos. It was also an air gunnery and bombing range, with targets on the land, floated 1 mile offshore and towed drogues in the air. A small range railway was in use to provide moving targets. The site was decommissioned in 1945 and returned to agriculture.