Family history implies that ROBERT GORDON AITKEN, was a 'Lieutenant in the Cavalary in India', from round about age, 18, i.e. +/- 1917.
It's very confusing to attempt to unravel which horse regiment Robert would have served with, as his "dates" fall within such changes that occurred at the time in the armies of India.
There was an Indian Army, which served until the time of partition, 1947. This had been formed, 1903, from the absorption of the three previous armies. The presidency armies of the Bengal Army, the Madras Army and the Bombay Army.
From 1903 -1947, in India, the army consisted of two entities, the Indian Army itself and The British Army in India.
If Robert did arrive as a cavalry man round about 1917, or 1918, which army would he have served with?