In 1875, two engineers, Irishman Stephen Alley and Glasweigan John Alexander MacLellan, formed a company in Bridgeton. Alley & MacLellan originally only produced engine parts such as valves and air compressors, but by 1880 they needed to expand due to a rise in business, and so moved to the Sentinel Works on Jessie Street in Polmadie, forming the Sentinel Engineering Works. This move also equipped them with a bold new energy that saw them company manufacturing entire steam engines rather than just components. However, it was tempered by the death of Alley, whose son, Stephen Evans Alley, took his place. The new partnership acquired several companies, including Simpson and Bibby of Horsehay in 1903. The Shropshire-based company made steam powered vehicles for road, and after the take-over production was moved to Polmadie, bring with them Simpson, Bibby and their designer Daniel Simpson.
By 1905 the first Sentinel Steam Waggon was produced; a Model 5 Ton Tipper, swiftly followed by the Model 6 Ton Flat. The mis-spelling of ‘wagon’ was deliberate, in order to set apart Sentinel products and illustrate their superiority. The company enjoyed another decade in Glasgow, before decided to move down South to Shrewsbury in 1915, with the Sentinel Steam Waggon No.1010 the last to be built in Glasgow. The original building on Jessie Street, while derelict, is category A-listed as it was believed to be the first steel-reinforced concrete building in Scotland.
The move from Glasgow proved difficult and costly, especially as the firm suffered a double blow in the separate deaths of John MacLellan and also Daniel Simpson. By 1918 the company was suffering financial difficulties, forcing Stephen Evans Alley to re-organise the company and rebrand it as the Sentinel Waggon Works.