Born: 1850 and died 1917 in France working for the Red Cross.
Son of: Maj Gen Richard Henry Crofton RA (1818-1897) and Francis Mary Crofton (nee Marsh, 1819-1906)
Brother of:
1. Amelia Alicia Anne Isaac (nee Crofton, 1849-19??) who married John Swinton Isaac.
2. Maj Richard Martin Crofton RHA (1854-1899) who married Marion Emma Heath (1856-1949).
3. Maj Henry Caldwell Crofton RHA (1856-1947) who married Helen Rose Ann Millman.
Duke married: 13th November 1883, Augusta Maude Lefroy (1854-1938) daughter of Gen Sir John Henry Lefroy RA, KCB, KCMG.
Duke and Augusta had issue:
1. Hugh Lefroy Crofton (1884-1917).
2. Philip Duke Crofton OBE (1886-1951), Commander RN, died 4 August 1954.  Buried St Giles, Bradford-on-Tone.
3. John Henry Crofton (1889-1914) known as Jack.
4. Sir Richard Marsh Crofton (1891-1955).  Prime Minister of Bahawalpur State in British India 1942 to 1948.
5. Patrick George Crofton (1899-1938).
6. Amy Dundas Crofton (1893-1975).
7. Hilda Frances Boles (nee Crofton, 1894-1943) who married Cmmd Geoffrey Coleridge Boles (1887-1976?).

We know of Duke from the following sources:
1. The book "Crofton Memoirs" by Henry Thomas Crofton, 1911.  
2. A note written by his grandson Jack Boles which is as follows:

Duke lived from 1850-1917. His family had lived at Lakefield, Mohill, County Leitrim in Ireland for many generations. He joined the Royal Navy and served on the China Station. He retired in 1897 and returned to farm at Lakefield and had a special interest in fruit growing. Although in his mid-sixties when the Great War started in 1914, he insisted on joining the Red Cross and died in France in 1917.

His son Sir Richard Marsh Crofton (1891-1955) had a daughter called Alison?

If you have any more information please do contact me.