warships, including the aircraft carrier USS Ranger (CV-4), were engaged in these Atlantic patrols at the time of Fleet Problem XXI, which ran from April 1st to May 17th of 1940, shrinking the wargame. Fleet Problem XXI was preceded in March with a mobilization exercise, where a simulated period of rising tension allowed the US Navy to practice distribution of secret orders, personnel recall, contingency planning, and other aspects of pre-war crisis. By April 3rd, the various participating fleet units had traveled to their starting positions, forming two teams: White, playing the US, operated out of Hawaii and Guam, while Black, playing Japan, operated out of major ports on the West Coast. On May 7, just days after the conclusion of Fleet Problem XXI, the fleet received orders to stay in Hawaii as a deterrent against Japan's growing aggressiveness. This decision was controversial; Admiral James Richardson, who was Commander in Chief, United States Fleet, protested that the fleet would be left vulnerable to air attack, as evidenced by years of successful air attacks simulated in the Fleet Problems. After months of objection, Admiral Richardson was eventually dismissed. The fleet stayed in Hawaii throughout the rising crisis with Japan, where it was attacked by Japanese air forces on December 7th, 1941. Fleet Problem XXII There were four proposals for the Fleet Problem scheduled for 1941, with hypothetical exercise areas in the Marshall Islands, Panama, the coast of Mexico, and the Northeastern Pacific. By December 3rd, 1940, Chief of Naval Operations Admiral Harold Stark had cancelled the exercise based on the worsening global situation. In the eighteen years since Fleet Problem I, the series of exercises had become high-profile enough that the cancellation made the front page of the New York Times. 21st Century Fleet Problems Fleet Problem XXIII Fleet Problem XXIII was the first to take place in the 21st century after the concept was revived by Admiral Scott Swift and the US Pacific Fleet. It centered around Carrier Strike Group One, led by the aircraft carrier USS Carl Vinson. Fleet Problems XXIV–XXVIII Details on these Fleet Problems are not widely public, although the US Navy did publicize that one Fleet Problem in 2021 did include a large number of unmanned vehicles led from a Zumwalt-class destroyer. Notes References Further reading Albert A. Nofi, To Train the Fleet For War: The U.S. Navy Fleet Problems, 1923–1940 (Newport, R.I.: Naval War College