The two ships frequently served together, first in the Atlantic Fleet in the 1910s. Both vessels were deployed to British waters after the United States entered World War I in April 1917 to reinforce the Royal Navy's Grand Fleet. They served in the Pacific Fleet in 1919–21, before both returned to the Atlantic Fleet. Much of their time in the Atlantic Fleet was spent conducting peacetime training exercises, along with taking midshipmen from the US Naval Academy on training cruises. "Wyoming" and "Arkansas" were heavily modernized in the mid-1920s, receiving more efficient oil-fired boilers to replace their old coal-fired models, thicker deck armor to protect against plunging fire, anti-torpedo bulges to increase their resistance to underwater damage, and anti-aircraft guns to defend against aerial attacks.