declared war on Germany as an "Associated Power" of the Allies. At this stage they were not at war with the other Central Powers. The United States Navy sent a battleship group to Scapa Flow to join the Grand Fleet and provided convoy escorts. In April 1917, the United States Army had fewer than 300,000 men, including National Guard units, compared to British and French armies of 4.1 and 8.3 million respectively. The Selective Service Act of 1917 drafted 2.8 million men, although training and equipping such numbers was a huge logistical challenge. By June 1918, over 667,000 members of the American Expeditionary Forces, or AEF, had been transported to France, a figure which reached 2 million by the end of November. However, American tactical doctrine was still based on pre-1914 principles, a world away from the combined arms approach used by the French and British in 1918. US commanders were initially slow to accept such ideas, leading to heavy casualties and it was not until the last month of the war that these failings were rectified. Despite his conviction Germany must be defeated, Wilson went to war to ensure the US played a leading role in shaping the peace, which meant preserving the AEF as a separate military force, rather than being absorbed into British or French units as his Allies wanted. He was strongly supported by AEF commander General John J. Pershing, a proponent of pre-1914 "open warfare" who considered the French and British emphasis on artillery as misguided and incompatible with American "offensive spirit". Much to the frustration of his Allies, who had suffered heavy losses in 1917, he insisted on retaining control of American troops and refused to commit them to the front line until able to operate as independent units. As a result, the first significant US involvement was the Meuse–Argonne offensive in late September 1918. April to June; Nivelle Offensive and French Army mutinies Verdun cost the French nearly 400,000 casualties, while the horrific conditions severely impacted morale, leading to a number of incidents of indiscipline. Although relatively minor, they reflected a belief among the rank and file that their sacrifices were not appreciated by their government or senior officers. Combatants on both sides claimed the battle was the most psychologically exhausting of the entire war; recognising this, Philippe Pétain frequently rotated divisions, a process known as the noria system. While this ensured units