The castle was built on an area of land believed to have been the site of an earlier Dún or fort, which may give its name to the locality.
He fought on the North-West Frontier in 1930 in the Guides Cavalry regiment of the British Indian Army, and was decorated for this service, and promoted to the rank of lieutenant-colonel.
He also served on the North West Frontier during World War II, and in the summer of 1941 led a squadron by the Khojak Pass in what is now Pakistan.
He retired from military service in 1947, the year the British Indian Army was stood down, having been decorated (Medal and Clasp).
Just over one year later the couple had their only child Edward John Carlos Plunkett, who would later succeed his father as 20th Lord Dunsany in 1999.
He and his wife stayed annually with Henry McIlhenny at Glenveagh in County Donegal, where he stalked deer and fished.