Birthplace:
- East Hundred Downs, Berkshire

Birthdate:
- 2 September 1848

Nationality:
- English

Height:
- 5 feet 10 inches

Family Background:
- Allin's father was John Allin Esq. "a private Gentleman of English family"

At Sandhurst:
- Yes

Foreign Languages:
- French

Career before Halifax:
- Ensign, 14th Foot, 14 August 1867 (purchase)
- to 72nd Highlanders by transfer, 25 September 1867
- Lieutenant, 20 July 1870 (purchase)
- to 78th Highlanders by exchange, 25 January 1871

Postings while in NS Command:
- Halifax, 11 March 1871 to 25 November 1871

All that is known of Allin's family background is that the father described himself on his son's birth certificate as "John Allin Esq. a Private Gentleman of English family". This probably indicates that he was affluent enough from private means not to have to work, and that he at least liked to think that his family was of some social pedigree. He listed his address as "Downs House, Wantage, Berkshire."

In June 1871, while in Halifax, Lieutenant Allin wrote the examination which was necessary for promotion to the rank of captain (rudimentary tests were required of all subalterns before they could purchase the rank above - ie. an ensign the rank of lieutenant, and a lieutenant the rank of captain). The Horse Guards informed Doyle after they had evaluated the results that Allin had "failed to answer one fourth of the questions put to him" even though the test "was one of easy character", and that therefore he had failed. He retired, still a lieutenant, in February 1875.