What is Navy coffee?
No one really knows for sure. Some naval vessels used to put salt in the coffee either to kill the bitterness (or to help stay hydrated), but it was neither a universal or permanent practice.
William Ewing, QM1(SW) USN (ret), Quartermaster E-6 has this to about the subject:
When navy coffee was 50% chicory, 50% cheap coffee (most of my career), it was a dying practice, based on previous coffee that was very bitter. Nowadays, the 50% chicory formula is not bitter enough to require that, and many ships get Starbucks, which they then mix with the chicory coffee to smooth the taste even more.
Now, for a while, Denny's had some bad coffee, and for over a year, my friends and I added salt to kill the bitterness and extra sugar to overpower the salt. Then Denny's switched blends to one not as awful, so we could drink it without salt. - Do Navy people put salt into their coffee?
Other sources say the complete opposite:
I had to make many, many pots of coffee as a mess crank (one who spends their first 90 days or so working on the mess decks. Think of it as KP for 90 days straight).
We used a large commercial drip coffeepot and coffee, period. No salt was added, at least I never added any. That it is strong comes from the fact that the Navy has no contracts with suppliers that have decent coffee.
It is possible that the salty taste does come from the fact that shipboard water is naturally salty. When a ship is in port, she's hooked up to local water. IIRC, ships at sea have a special desalinization process that isn't perfect, but it comes fairly close. - How the Real Men in the Navy Make Their Coffee
For a number of years, I used to put salt in the grounds to help remove the bitterness of the coffee. Please not that this was not navy coffee and I was making a 100 cups at a time. No one ever complained, but that might have been to sure dumb luck too.
The Urban Possum has this to say about Navy Coffee:
Use an economy-brand coffee. Mother Parker's, for example, or Chase & Sanborn. If you have to talk in terms of roasts, these brands are a light to medium--perfectly acceptable to a majority of people. Their virtue is that they're cheap--hey, it's Navy coffee. We're talking government suppliers here.
Use 2 level tablespoons for each 8-ounce cup. The standard measure for coffee is 1 level tablespoon for a 6-ounce cup. The power of Navy Coffee does not derive from the strength of the roast, but from the amount of coffee used, so as you can see, this one is stronger than most. Some old chiefs like the coffee so strong that it actually seems chewy (that comes from the tannins in the coffee and their effects on the tooth surface), but we don't need to go quite that far.
Salt the grounds before you begin brewing. Salt, as in ordinary table salt. The measurement is a pinch, which is about 1/8th to a maximum of 1/4 teaspoon per 5 cups brewed. This is the secret to True Navy coffee: the salt will cut the initial bitterness of the coffee, but takes nothing away from the aroma. Don't worry too much about the taste, Navy coffee won't taste salty unless you use too much of it.
As a side note, the navy often employs the term a Cup of Joe to their Navy Coffee. Where this tradition first came into use is unknown but some believe it was due to the Secretary of the US Navy, Admiral Josephus “Joe” Daniels who abolished wine (or alcohol) on Navy ships in 1914. Thus, coffee (the next best thing) was the beverage of choice for the sailors.