From Wikipedia

Captain Cook

Part One

On 16 February 1768, the Royal Society petitioned King George III to finance a scientific expedition to the Pacific to study and observe the 1769 transit of Venus across the sun. Royal approval was granted for the expedition, and the Admiralty elected to combine the scientific voyage with a confidential mission to search the south Pacific for signs of the postulated continent Terra Australis Incognita (or "unknown southern land").

The Royal Society suggested command be given to Scottish geographer Alexander Dalrymple, whose acceptance was conditional on a brevet commission as a captain in the Royal Navy. However, First Lord of the Admiralty Edward Hawke refused, going so far as to say he would rather cut off his right hand than give command of a Navy vessel to someone not educated as a seaman. In refusing Dalrymple's command, Hawke was influenced by previous insubordination aboard the sloop HMS Paramour in 1698, when naval officers had refused to take orders from civilian commander Dr. Edmond Halley. The impasse was broken when the Admiralty proposed James Cook, a naval officer with a background in mathematics and cartography. Acceptable to both parties, Cook was promoted to Lieutenant and named as commander of the expedition.