Renamed as His Majesty 's Bark the Endeavour , she left Plymouth in August 1768 . After sailing around Cape Horn she reached Tahiti to see the 1769 transit of Venus across the Sun . Renamed and commissioned as His Majesty 's Bark the Endeavour , she departed Plymouth in August 1768 , rounded Cape Horn , and reached Tahiti in time to observe the 1769 transit of Venus across the Sun .