He was elected a Fellow of the Royal Society in May, 1770 for carrying out "a series of curious experiments to determine the different degrees of cold at different depths in the Sea".

He was also in charge of creating a navy from scratch to fight on Lake Champlain, and that small fleet routed the Americans under Benedict Arnold.

Douglas is credited by many, including Sir Charles Dashwood (a midshipman present at the time who later became an admiral himself), for having the idea for the manoeuvre, but it is a subject of much debate.

There is a great deal of confusion regarding the identity of Sir Charles' third wife, whose last name has been variously reported as Baillie, Grew, and Brisbane.

The case is made famous because of a letter Lydia had written to Adam Smith, a friend and distant relative of Sir Charles, requesting his assistance in reconciling the father and daughter.

Sir Charles was known as a mechanical genius,[2] and many of his suggestions for improvements on naval vessels, including the substitution of flintlocks for matches, were adopted by the Admiralty for the entire Royal Navy.