via Harry Reid - Aitken was the youngest of the six Ballantine brothers and was 38 when war broke out, so was liable for conscription with 40 being the maximum age (Harry, my grandfather, just missed it by a matter of months). Aitken worked as a coal and steel importer. 
For some unknown reason he was recruited by the South Wales Borderers regiment (as opposed to a Scottish regiment) in late 1914 as a second lieutenant and for the first 6 or 7 months was moved round the country in training and preparation for fighting - bases included Liverpool, Hornchurch and Pembroke.
The Gallipoli campaign commenced in April 1915 but Aitken's regiment didn't get involved until August 1915 but apparently spent the following six months in action, until withdrawal in January 1916 when the Allies gave it up as a bad job.
Aitken and his regiment in fact were transported to Turkey by a P&O liner which had been taken over by the government as a troop carrier, and apparently it was a very comfortable cruise across the Med!
Aitken survived the fighting but lost his hearing as a result of the noise from the big guns being used against the Ottomans. He was invalided out of the army on return and eventually died from cancer in 1937, aged 61. Apparently he was awarded three medals for action in the Gallipoli campaign.
Aitken was a bachelor and lived with his elder sister, Minnie, at 99A Eldon Street in Greenock, which still stands today. He wrote regular postcards to Minnie, telling her where he was in the UK while in the army and headlines on what was happening, plus any needs he had. 

Served at Gallipoli. Duncan Kerr of the Argyll's talks about Aitken in his letter home "I hear that Aitken Ballantyne is out here, an officer in the Scottish Rifles and that he has been recommended for the DCM on account of some valorious services - they are the type of men we want for officers"

Mention of Aitken in War Diary HERE

Newspaper Clippings relating to Aitken Ballantine

Ballantine, Aitken

Aitken Ballantine cricket

Aitken Ballantine MiD