On February 9, 1942, during World War II, most of Arizona moved to Mountain War Time but a few western Arizona border communities observed Pacific War Time. President Franklin Delano Roosevelt instituted War Time (daylight saving time) that year. On January 1, 1944, most of Arizona returned to MST . Some western Arizona border communities remained on Pacific War Time. Also, railroads, air lines, bus lines, military personnel and some engaged in interstate commerce continued to observe Mountain War Time in line with a federal law.