He was a merchant navy officer

Young Ernest Shackleton was just 16 years old when he was allowed to quit school and sail away. Because he lacked the funds to either join the commercial marine cadetships or the Royal Navy at Britannia as a cadet, he decided to take up an apprenticeship "before the mast" on a sailing ship. The North-Western Shipping Company's square-rigged sailing ship Hoghton Tower served as his first berth. He spent the next four years honing his craft at sea while traveling the globe and meeting fascinating new people. He became a qualified second mate in August 1894 and accepted a position as the third officer on a tramp steamer of the Welsh Shire Line. He achieved his status as the first in just two years. In just two years, he received his first mate's title, and in 1898, he received his master mariner's license. As a result, he met the requirements to assume command of a British ship anywhere in the world.

Ernest Shackleton served as a young officer on the Union-Castle Line in 1898, which transported people and mail regularly between Southampton and Cape Town. After the Boer War broke out in 1899, he shifted to the troopship Tintagel Castle and exchanged mail and passengers for troops. He met army lieutenant Cedric Longstaff here in March 1900. Llewellyn W. Longstaff, Cedric's father, provided financial support for the National Antarctic Expedition that was being planned at the time in London.

He was able to speak with Longstaff because of his relationship with the son. Longstaff was so taken aback by Shackleton that he recommended him to Sir Clements Markham, the expedition's commander. On February 17th, 1901, Shackleton was officially named the third officer of the expedition ship Discovery. On June 4th, when he was commissioned into the Royal Navy as a sub-lieutenant in the Royal Naval Reserve, his time in the Merchant Navy practically came to an end.