The 1919 Forty Hours general strike is most often remembered for the ‘Bloody Friday’ police riot in Glasgow on 31 January. The article argues that its true significance lies elsewhere. It was as a political strike that carried forward the lessons of the wartime shopstewards movement into the postwar period, that drew organisationally on the experience of Bolshevik revolution in establishing area ‘social committees’ and provided a model for the development of Councils of Action as deployed in 1920 and 1926. The strike’s success in mobilising support across Britain impacted powerfully on the policies of the postwar coalition government. It was instrumental in reversing plans for a deflationary budget in favour of expenditures on housing, pensions and health – described by Lloyd George as ‘insurance against Bolshevism’. On Clydeside the experience of the strike, and the military occupation it provoked, marked a defining moment in the creation of a new working-class identity bridging workplaces and communities and consolidating support for socialist politics.