During the First World War, which battle resulted in the British suffering 60,000 casualties on the first day?

The First World War, lasting from 1914 to 1918, was a devastating conflict involving many nations across Europe and beyond. One of the most infamous battles of this war was the Battle of the Somme, which began on July 1, 1916. The aim of the battle was for the British and French forces to break through the German lines on the Western Front. Sadly, the first day of the Somme is remembered as one of the bloodiest days in British military history. On that single day, the British Army suffered approximately 60,000 casualties, including around 20,000 deaths. This staggering loss of life makes the Battle of the Somme a particularly significant and tragic event in British history, and the reason why it's the correct answer. The other battles listed, while important in their own right, occurred in different time periods. Agincourt was a medieval battle in 1415, Waterloo in 1815, and El Alamein during the Second World War in 1942.