In 1953, explorers Sir Edmund Hillary and Tenzing Norgay were the first humans to successfully climb Everest. Explorer (explorer) was announced in honor of that achievement. The Explorer I still has a consistent identity of only the hour, minute and second hands, and its lean and simple design contributes to long sellers. In 1971, Explorer II was announced as a model for cave explorers. It has a 24-hour hand to distinguish between day and night even in dark caves. The Explorer II, worn by Italian climber Reinhold Messner at the time of the first ever climb to Everest anoxic in Mankind, demonstrated its ability in extreme conditions.