He enlisted in the Argyll and Sutherland Highlanders on the same day as Peter Burr 6537 and a William Mackay 6529 from Glasgow. Their military numbers are so close they must have stood in the queue together as they waited to enlist.
Magnus was initially sent to Tain for his military training, he was then transferred to the 13 Battalion Argyll and Sutherland Highlanders at Dorking in Surrey where he served with ‘C’ Company. In June 1915 the 13 Argylls were transferred to Tain to become the Argyll and Sutherland Highlanders training battalion. Magnus remained with the 13 Battalion until he was sent to France to join the 11 Argylls in late 1915.
In March 1916 the 11 Argylls were in reserve trenches, near Loos village on routine trench holding duties. The battalion was busy improving trenches and laying floorboards in good weather, in what was considered to be a fairly quiet sector of the front. The battalion was to relieve the 7 Battalion Inniskillens in the front line trench on the night of the 19 of March. As the preparations were being to move into the front line, enemy shellfire fell on the Argyll’s positions killing a number of men. A bomb store was also hit killing the five sentries stationed there, one man was wounded he died later.Private Magnus Mackay was one of the sentries killed in the bomb store, he was buried in Loos village by his comrades; he was 18years of age. He was the first of Alex ‘Bolt’ Mackays sons to be killed, the stories of his other sons Angus and Donald appear elsewhere .