 Complete the following phrase:  On 1 July 1916, the first day of the Battle of the Somme, the British Army endured the bloodiest day in its history, suffering 57,470 casualties and 19,240 dead; nine Victoria Crosses were awarded for action on that day. Most of the casualties occurred in the first hour of the attack. The entire Somme offensive cost the British Army almost half a million men. The war was not just fought on land; the First World War saw major naval battles as well as the first large-scale use of military aircraft. The war at sea was mainly characterized by the efforts of the Allied Powers in blockading the Central Powers by sea. In return, the Central Powers attempted to break that blockade and establish an effective blockade of the British Isles and France with U-boats and raiders. The largest naval battle of the First World War was the 