Navy Strength

Where to start with this question?

For one thing, the setter has got confused between alcohol by volume (ABV) and proof.

In the 18th century, so the story goes, officers in the Royal Navy were concerned about their gin (or rum) being watered down – either by unscrupulous merchants, or by ratings stealing the odd snifter and replacing it with water. Then they discovered that gunpowder that had been soaked in spirits would still light, as long as the spirit had an ABV content of 57% or higher. (The actual value is more like 57.15%.) From that day forward, they insisted on their spirits having an ABV content of at least 57%, so that they could test it on board ship.

This naturally became known as 'navy strength', and it also became known as '100 degrees proof'.

This story is related on Wikipedia, as well as on any number of websites selling navy strength spirits (such as this one, for example). So I'm fairly confident that it's true.

The first problem with the question is that navy strength is not 57% proof or above; it's 57% ABV or above, or 100% proof and above. (Yes, it is possible to have spirits that are more than 100% proof. 57% is very close to 4/7, so 100% ABV is very nearly 175 degrees proof.)

Similarly, a normal strength (as opposed to navy strength) is 40 to 43 percent ABV, not 40 to 43 degrees proof. 40% ABV equates to approximately 70 degrees proof.

The second problem with the question is that any number over 56 was allowed. I'm all in favour of leeway being given when appropriate, and it's nearly always better to err on the generous side ... but this is ridiculous. The person who got this question in the quiz I took part in answered "70%", and was given the points.

Gin and rum are rarely sold at strengths much higher than 57%. If you see a brand that claims to be navy strength, it will almost certainly have a claimed ABV rating of between 57% and 60%. (Four Pillars gin, the one in my example, is 58.8%.)

A far better way of asking this question (IMHO) would be "The term 'navy strength' refers to spirits that have an ABV rating of at least what percentage?" You could allow leeway on this, by all means; I would suggest 2 or 3 percent either way. But not "any number over 56".

In the United States, 100 degrees proof equates to 50% ABV. So a spirit produced in the USA will have a slightly higher proof rating than a similar–strength one produced in the UK.