Untrue.

1.The OED does not record the term "monkey" or "brass monkey" being used in this way.

2. The purported method of storage of cannonballs ("round shot") is simply false. Shot was not stored on deck continuously on the off-chance that the ship might go into battle. Indeed, decks were kept as clear as possible.

3. Furthermore, such a method of storage would result in shot rolling around on deck and causing a hazard in high seas. Shot was stored on the gun or spar decks, in shot racks—longitudinal wooden planks with holes bored into them, known as shot garlands in the Royal Navy, into which round shot were inserted for ready use by the gun crew.

4. Shot was not left exposed to the elements where it could rust. Such rust could lead to the ball not flying true or jamming in the barrel and exploding the gun. Indeed, gunners would attempt to remove as many imperfections as possible from the surfaces of balls.

5. The physics does not stand up to scrutiny. The contraction of both balls and plate over the range of temperatures involved would not be particularly large. The effect claimed possibly could be reproduced under laboratory conditions with objects engineered to a high precision for this purpose, but it is unlikely it would ever have occurred in real life aboard a warship.


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Early references to "brass monkeys" in the 19th century have no references to balls at all, but instead variously say that it is cold enough to freeze the tail, nose, ears, and whiskers off a brass monkey; or hot enough to "scald the throat" or "singe the hair" of a brass monkey. All of these variations imply that an actual monkey is the subject of the metaphor.

The first known recorded use of the phrase "brass monkey" appears in the humorous essay "On Enjoying Life" by Eldridge Gerry Paige (writing under the pseudonym "Dow, Jr."), published in the New York Sunday Mercury and republished in the book Short Patent Sermons by Dow, Jr. (New York, 1845)
"When you love, [...] your heart, hands, feet and flesh are as cold and senseless as the toes of a brass monkey in winter."


The second known published instance of the phrase appeared in 1847, in a portion of Herman Melville's autobiographical narrative Omoo:
"It was so excessively hot in this still, brooding valley, shut out from the Trades, and only open toward the leeward side of the island, that labor in the sun was out of the question. To use a hyperbolical phrase of Shorty's, 'It was 'ot enough to melt the nose h'off a brass monkey.'"

The first recorded use of freezing a "brass monkey" dates from 1857, appearing in C.A. Abbey, Before the Mast, p. 108: "It would freeze the tail off a brass monkey".