This man served as MARTIN, so is "mis-filed" in the MAR section of the WW1 Service Records (WO 363).
His mother and half-siblings are all surnamed MARTIN.

George joined the Argyll & Sutherland Highlanders in April 1913, declared age 18y 2m, born Kelty, Fifeshire. Served as Pte 1883. Killed in action 1915.

Home address: Nasmyth(?) Place, Kelty;
Mother: Isabella;
Half-brothers: Alan (c1901), Andrew (c1903) & James (c1909);
Half-sisters: Kate (c1906), Agnes (c1907) & Marion (c1912).

Anc****y, MAR, pages 153144 - 153164