David Dundas, was L.Col. David Watson’s nephew. He was the third son of Robert Dundas and Margaret Watson. His father was a merchant in Edinburgh, a senior member of the family of Dundas and of Arniston. David was born in 1735. His uncle arranged a placement for him as a Board of Ordnance cadet, to join William Roy on the Military Survey. He was made assistant quartermaster in 1752 ( aged 17) and took charge of the eastern part of the Lowlands Survey which was completed by 1755. He was then commissioned and there followed a very distinguished army career culminating in quartermaster-general in 1797 and commander-in-chief in 1809. A great advocate of officer training, he wrote the first manuals on the subject.
He became 2nd Baronet Arniston and a privy councillor. He was lifelong friend to William Roy as well as a military colleague.