Conversation so far:
What happened in 1903?
As the first significant person to return from the Antarctic, he found that he was in demand.
In demand for what?
the Admiralty wished to consult him about its further proposals for the rescue of Discovery.
What are some other interesting aspects about this article?
In search of more permanent employment, Shackleton applied for a regular commission in the Royal Navy, via the back-door route of the Supplementary List.

Question: Why was he applying for employment?
Self-contained rewrite: Why was Ernest Shackleton applying for employment after his Antarctic return?