With the Great War edging into its third calendar year, British Prime Minister Herbert Asquith introduces the first military conscription bill in his country’s history to the House of Commons on January 5, 1916.

Lord Horatio Herbert Kitchener, Britain’s secretary of state for war, had warned from the beginning that the war would be decided by Britain’s last 1 million men. All the regular divisions of the British army went into action in the summer of 1914 and the campaign for volunteers based around the slogan “Your King and Country Need You! began in earnest in August of that year. New volunteers were rapidly enlisted and trained, many of them joining what were known as Pals battalions, or regiments of men from the same town or from similar professional backgrounds.

Though the volunteer response was undoubtedly impressive—almost 500,000 men enlisted in the first six weeks of the war alone—some doubted the quality of these so-called Kitchener armies. British General Henry Wilson, a career military man, wrote in his diary of his country’s “ridiculous and preposterous army” and compared it unfavorably to that of Germany, which, with the help of conscription, had been steadily building and improving its armed forces for the past 40 years.

By the end of 1915, as the war proved to be far longer and bloodier than expected and the army shrank—Britain had lost 60,000 officers by late summer—it had become clear to Kitchener that military conscription would be necessary to win the war. Asquith, though he feared conscription would be a politically unattractive proposition, finally submitted. On January 5, 1916, he introduced the first conscription bill to Parliament. It was passed into law as the Military Service Act later that month and went into effect on February 10.

Britain had entered the war believing that its primary role would be to provide industrial and economic support to its allies, but by war’s end the country had enlisted 49 percent of its men between the ages of 15 and 49 for military service, a clear testament to the immense human sacrifice the conflict demanded.