There is an aphorism – Repeat a lie often enough, and it becomes the truth. When it comes to rum promoting itself as “Navy Strength” at a hearty 57% ABV, this couldn’t be truer.
The simple fact of the matter is that Britain’s Royal Navy issued its rum at 54.5% ABV.
To repeat: navy strength is 54.5% ABV. It’s that simple.
(One could argue that “navy strength” doesn’t necessarily refer to Britain’s Royal Navy. But honestly– what other navy was remotely famous for its rum?)
So, how is it that so many brands, big and small, release rum (and gin) at 57% ABV and label them “navy strength?”
The answer lies in a misunderstanding of British spirits terminology. In brief, a “proof” spirit is 57.14% ABV in modern terms. A spirit at exactly that strength was called a “proof spirit” or “at proof.”
Anything stronger than proof strength (57.14% ABV) was dubbed overproof. Anything below proof strength was underproof. (For conciseness, I shall omit an explanation of “degrees proof” math here. Should you nonetheless wish to dive in, read this story.)
With this elementary understanding of what proof, underproof, and overproof mean, what did the Royal Navy say about the strength of the rum it issued to sailors? The navy’s 1939 victualling manual [i] (basically, instructions for provisioning its sailors) is quite clear:
… and the issuing strength is 4.5 under proof. This latter strength was fixed on the 19th February 1866.
A rather lengthy letter [ii], written by the Royal Navy in 1965, provides a bit more context:
“Proof” spirit is 57% spirit and/43% water by volume. In the absence of evidence to the contrary, it is assumed that Service rum was issued at about this strength until 1866 when the issue strength was fixed at 95.5 Proof (or 4.5 under-Proof).
In brief, the navy itself wasn’t sure what strength it issued rum at before 1866, but it may have been proof strength. However, from 1866 onward, it was “4.5 under-Proof”. In the “degrees proof’ math system, “95.5 Proof” works out to 54.5% ABV.
As an aside, it’s worth highlighting that the navy’s manual calls its rum under proof. If “proof strength” is the minimum strength required for gunpowder to ignite, then tales about “proving” the strength of navy rum with gunpowder don’t hold up well to historical scrutiny. Also: Labels that declare both “navy strength” and “overproof” are doubly wrong.
Can we empirically verify that Royal Navy rum was issued at 54.5% ABV? Yes! There are two well-known real-world examples to draw from.
The Black Tot Last Consignment rum is honest-to-goodness Royal Navy rum, stored in flagons for many years before being bottled by Elixir Spirits. Its strength: 54.3% ABV. The 0.2% discrepancy is negligible given that it was originally issued over 50 years ago.
The second example is the original Pusser’s Rum, released in 1979. After receiving permission from the Royal Navy, Charles Tobias set out to faithfully reproduce the navy’s recipe. The original Pusser’s release was at 54.5 percent ABV. The brand’s more recent Gunpowder Proof release is also at 54.5% ABV.
Why do so many brands get navy strength wrong? I suspect someone confused “navy strength” with “proof” when releasing a “navy strength rum” – at 57% ABV. [iii] A mistake in the wild has a powerful ability to propagate, and the rest is history.
It’s worth noting that some new brands have taken the time to get it right. Among them, Lost Years Navy Strength Rum and Worthy Park’s 109 Proof. (The latter’s 109 refers to the strength in the US proof system, which equals 54.5% ABV; the brand specifically targeted this strength for historical accuracy.)
As for rums selling at 57% ABV and calling them navy strength? A simple label change to instead call them “proof strength” is all that’s needed to ensure historical fidelity.
I understand that some out there might say, “Why does this matter? It’s just a harmless bit of marketing fluff.” My response: History and facts matter.
I well understand that most brands don’t have a historian on staff to vet their marketing, so many mislabeled “navy strength” rums aren’t intentionally misleading. However, in highlighting this widespread misunderstanding here, I hope to help brands get things right going forward. As another famous saying goes – A journey of a thousand miles begins with a single step.
[i] Victualling Manual – BR(93), British National Archives ADM 234/19, 1939
[ii] Historical information on the issue of rum in the Royal Navy, British National Archives ADM 114/152, 1965
[iii] One source suggest that the first usage of “navy strength” for branding purposes was Plymouth Gin in 1993. (Michael Nolledo, InsideHook.com “What “Navy Strength” Booze Means, and Where to Find It”)