Filed as MARSH in the WW1 Service Records (WO 363):

Henry St George DYKE-MARSH, born 1894 (Windsor)
Mother: Edith
Home: Wokingham, Berks

A Science student, he joined the Royal Engineers 14 November 1916 and was transferred to the Meteorological Section in 1917.
Regt No: 225090
De-mobbed in 1919

Anc****y, MAR, pages 182945 - 182962