He was the middle of three shipbuilding and engineering brothers in Glasgow who revolutionised heating, cooling and ventilation in shipping accommodation, railways, aircraft and public buildings around the world .

[7] In 1901 the three brothers set up their own firm, Thermotank, based in Glasgow with works coming next to the Clyde at Govan in 1908, and later with branches and agencies overseas.

In 1913 William M Stewart married Jessie Brown of Newlands, Glasgow[8] and settled in Lochbrae House, overlooking St Germain's Loch, Bearsden.

An appreciation of him in the Glasgow Bailie magazine of 23 September 1922 describes his career to date:- "Educated at Allan Glen's and at the University where he studied engineering.

"[1] Stewart died in 1926 at home in Lochbrae House, Bearsden; with the younger of his two bachelor brothers continuing to lead the Thermotank businesses.