Germany became the first country to adopt Daylight Saving Time on April 30, 1916, to conserve coal for the war effort during World War I.

Daylight Saving Time emerged as a strategic response to severe energy shortages during World War I. On April 30, 1916, the German Empire and Austria-Hungary became the first nations to implement the policy, advancing clocks by one hour to reduce coal consumption for electric lighting and redirect that fuel toward munitions production and heating.The concept was not entirely new. New Zealand entomologist George Hudson had proposed a two-hour time shift in 1895 to gain more daylight for insect collecting, and British builder William Willett had advocated for "Summer Time" in 1907 to prevent daylight waste. However, the economic pressures of global conflict provided the impetus for official government adoption.The United Kingdom implemented the Summer Time Act on May 21, 1916, just weeks after Germany. The United States adopted Daylight Saving Time in 1918 through the Standard Time Act, though it proved unpopular with farmers and was repealed nationally after the war ended. Modern research by institutions like the American Academy of Sleep Medicine continues to examine DST's effects on health and energy consumption, with its long-term efficacy remaining a subject of ongoing debate.