[2] During his education, Gregg was an active and capable sportsman, playing cricket, tennis, baseball, swimming and ice hockey at university.

[2] Promoted temporary captain on 23 March 1916, he was an acting major for just over a month in 1919, was wounded in the field, and was awarded the Military Cross for gallantry on 24 September 1918.

He untiringly attended to the wounded under heavy enemy fire until the last man was cleared, and showed great coolness and devotion to duty.

[6]Returning to Australia, Gregg was appointed resident medical officer at Sydney's Royal Prince Alfred Hospital (RPA).

Gregg noticed a high incidence of congenital cataracts in infants arriving at his surgery – two to three times the normal rate that would be expected from hereditary factors.

[12] On 15 October 1941, Gregg delivered a paper, Congenital Cataract following German Measles in the Mother, to the Ophthalmological Society of Australia in Melbourne which published it in its journal, Transactions.