During the Second World War, the Mourne Mountains, Co. Down provided a training ground for troops as well as a hazard to military planes on training exercises.
On 22nd April 1941, His Royal Highness the Duke of Gloucester and senior military officers watched soldiers training in and around the Yellow River in the Mournes.
An image in the guidebook for U.S. GIs showed troops the sprawling Mourne Mountains in Co. Down with neat hedgerows, thatched cottages, and picturesque valleys.
Many aviation incidents that occurred in Northern Ireland involved planes in training exercises often in poor weather and over the high ground of the Mourne Mountains.