The Challenger set out to accomplish... colonization. colonization. fighting an enemy. fighting an enemy. biological exploration. biological exploration. soundings of the ocean.

The Challenger set out to accomplish biological exploration.

Explanation:

The Challenger Expedition was a sea expedition devised by Professor Charles Wyville Thomson and his student John Murray. The expedition began in 1872 and was supported by the British government and the Royal Navy of Great Britain.

The expedition was made inspired by Darwin's voyages and had as main objective to make a biological exploration of the ocean, researching, mainly, the possibility of existence of marine life below 549 meters, where it was believed that life was impossible due to the high pressure and the total absence of light.