Josephus Daniels (1862–1948) was appointed Secretary of the U.S. Navy by President Woodrow Wilson in 1913. Among his numerous reforms of the Navy was the abolition of the officers’ wine mess. From that time on, the strongest drink aboard navy ships was coffee and over the years, a cup of coffee became known as "a cup of Joe".

I seen on http://www.bbc.co.uk/dna/h2g2/A1300410 That

"In 1914, the secretary of the US Navy, Admiral Josephus 'Joe' Daniels abolished the officers' wine mess. From that time on the strongest (and apparently therefore the drink of choice) on board navy ships was coffee. It was dubbed 'a cup of Joe' after the secretary."

I dont know if this is true but its an interesting story.

I am telling the truth, When men would go out to battle they would need something to get them going, so they would ask for a cup of coffee by calling it a cup of joe
Jolt of Energy from the caffin

Unfortunately, there is no way to answer this question with ia "the slang term joe for coffee came from..." I can, however relate that the first answer is highly unlikely. The most plausible (and therefore likely) anwer according to 2 etymologists on the web I consult is that "Joe" is related to either the use of Joe as the common man (coffee is the common man's drink) or as a derivative of Java. Boring I know!

The previous response referenced a story that I've also heard used to explain a "cup of joe." However, while it is a great story, there is no support for it.
I go to 2 etyomology (study of word origin, though the literal breakdown is "study of what is real") sites on the web when I want to know about word/phrase origins. Both of them are written by professionals who specialize in etymology.

WorldWideWords ( http://www.worldwidewords.org/qa/qa-joe1.htm ) indicates that the banning of the wine mess theory is unlikely because, " Cup of joe appears in the written record in 1930 but the order to ban alcohol—General Order 99—was issued on 1 June 1914." Another point the author makes is that wine mess halls were only for officers, not the common sailor,, so why would the common person be bothered enough to start a slang term.? This slang was (and is) used by everyone, not just a special group of people (the officers).

The Word Detective ( http://www.word-detective.com/041899.html ) is pretty much in agreement. WorldWideWords agrees with the Word Detective, who suggests that "joe" as slang for coffee might be derived from "Joe" as a synonym for "the common man," as in "regular joe." They do differ on whether
"GI Joe" for enlisted men was in use at that ttime. Even if it wasn't, US citizens jhad been using "the common Joe" and other such phrases for a whle when the ft instance of joe for coffee is written.

Of additional interest; WWW writes: It is significant that an early example appears in 1931 in the Reserve Officer’s Manual by a man named Erdman: “Jamoke, Java, Joe. Coffee. Derived from the words Java and Mocha, where originally the best coffee came from”.

Cup of Joe

Josephus Daniels (18 May 1862-15 January 1948) was appointed Secretary of the Navy by President Woodrow Wilson in 1913. Among his reforms of the Navy were inaugurating the practice of making 100 Sailors from the Fleet eligible for entrance into the Naval Academy, the introduction of women into the service, and the abolishment of the officers' wine mess. From that time on, the strongest drink aboard Navy ships could only be coffee and over the years, a cup of coffee became known as "a cup of Joe".

maybe there was a guy named Joe who used to go around relieving himself in peoples coffee cups, so they were drinking a cup of Joe....

Really, it could happen.

Here is another explanation http://www.volcanicacoffee.com/.../

Being from North Carolina, I like to believe that cup a joe (the namesake of the oldest coffee company in the state) originated with Josephus Daniels. Although the chronological evidence is unlikely, there is historical evidence to suggest that the banning of alcohol on Naval vessels was part of the origin. The coffee shop currently serves a frozen coffee concoction known simply as "Joe Juice" which can be traced to Daniels' insistence that if those in the Navy didn't like coffee, they should just drink fruit juice. Certainly the current "joe juice" isn't fruity...but it certainly makes for a nice story.

In the mid 19th Century, this term appeared in Mark Twain's writing about his experiences mining in the Nevada Territory.
While working on the Virginia City Enterprise, Twain had met a ranch family who befriended him and he became very close to the men in the family. The father, a hard working rancher had three sons who often would want to cut loose after a hard week of chores.
The father, hoping to prevent his sons from getting into too much trouble when they went into town, decided his boys wouldn't listen to his words of warning. He made them rise at dawn on Saturday and work a full day doing the most difficult chores. The sons were usually too worn out to even consider going into town by sun down. His youngest son, decided to out wit his father. Little Joe Cartwright drank alot of coffee on the ranch, the Ponderosa all day Saturday to keep him awake when he went into town to romance the local girls. Twain reported this in The Celebrated Jumping Frog of Calaveras County in a page that is often left out. He describes how "Little Joe" even fed the frogs coffee to help them jump higher.
This became the origin of "A CUP OF JOE".

In volume I, chapter xvi of Dickens' Great Expectations, the following is written: "When, at last, she came round so far as to be helped down stairs, it was still necessary to keep my slate always by her, that she might indicate in writing what she could not indicate in speech. As she was (very bad handwriting apart) a more than indifferent speller, and as Joe was a more than indifferent reader, extraordinary complications arose between them, which I was always called in to solve. The administration of mutton instead of medicine, the substitution of Tea for Joe, and the baker for bacon, were among the mildest of my own mistakes."

While perhaps not the true origin of the expression, this phrase at least predates the other explanations here and would give whomever first applied the phrase something of an intellectual underpinning.

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