Why is a cup of coffee called a cup of joe?

In 1913, The US navy use to have the same habits as the British Navy. Drinking too much rum. They would drink rum every hour or so, that was the tradition. But it soon changed when the Secretary that year was Joseph(Joe) Daniels, a non-alcohol man, he prohibited any alcohol on any American navy ship. The coffee was the strongest drink for the sailors, they didn’t like it but nothing else was much better. So they started calling their coffee mugs a cup of Joe.

Did you know rum was often used by the politicians in that era to persuade people to vote for them. They would often treat them with Bumbo(better rum than the navy’s) at the elections.