to six months hard labour at Wormwood Scrubs. After he had served his sentence he was refused the amnesty made available after the war to most conscientious objectors, rearrested and sent to Carmarthen jail. The SWMF campaigned for his release and to this end secured his election in absentia as checkweighman at Mardy Colliery, one of the most militant collieries in the Rhondda valleys. To add to the pressure on the authorities Horner began a hunger strike, refusing both food and water. After six days this combination of tactics secured his release in May 1919. Member of the Communist Party of Great Britain and Trade Union leader Horner became a founding member of the Communist Party of Great Britain (CPGB) in 1921. He was part of the nucleus of Communists who founded the National Minority Movement in August 1924. Elected to the Executive Committee of the SWMF in 1926, he played a leading role in the ten-month-long countrywide lockout of coalminers in 1926, following the General Strike. During the early years of the 1930s Horner's disaffection with the CPGB's policy towards trade unions was such that he faced expulsion from the party. "Hornerism" was denounced by the CPGB Executive as a deviation from the Comintern's (Communist International) Third Period or "Class Against Class" line. Horner travelled to Moscow in 1931 to appeal against his proposed expulsion before a Comintern commission. The verdict, which identified mistakes on both sides, was sufficiently equitable for Horner to feel he could comply with the required public admission of his alleged mistakes. In 1932, imprisoned on trumped-up charges of unlawful assembly, Horner took the opportunity availed to him as Cardiff prison librarian to study The Art of War by Carl von Clausewitz, a work which would significantly influence his future approach to formulating Union strategy and class politics in general – often leading to further conflict with the CPGB Executive. His increased strategic awareness would leave him strongly inclined against indiscriminate outbreaks of industrial action jeopardising the Union's strength and ability to win concessions for its members. Having stood unsuccessfully as a CPGB Parliamentary candidate in the 1933 Rhondda East by-election, Horner was elected President of the South Wales Miners' Federation in 1936. He served until 1946 and was instrumental in effecting a series of compromise settlements with the coal owners that rationalized industrial relations and improved wages and conditions. During the Second World War,