I watched Master and Commander for the first time the other day and fell in love with it. I know the story is fiction; but rooted in historical accuracy. I suppose I should put a spoiler warning here for those who have not seen it.
The main question that I came away with after watching the movie is whether the deception at climax of the film would have been “legal” at the time in regards to the rules of engagement.
I am very interested in naval history but don’t know much about laws or treaties that govern/governed naval warfare. I’m not sure if “rules of engagement” is even the right term for what I’m asking, so I hope this question makes since. Also, I figure that war is was and tactics are not always limited to what is acceptable at the time. Anyways, I can probably boil this down into three parts:
Was the disguising of a warship allowed under the rules of engagement at the time and if so, what were the specific rules?(ie. did you have to fly a flag, declare yourself at a certain time, etc.)
Is there a real/famous example of this tactic being used in the time this story would have taken place?
How have deception and concealment in naval warfare evolved and been governed over time?
The exploits of Jack Aubrey are largely based on those of Thomas Cochrane. In the book, Master and Commander, Aubrey disguises his ship, HMS Sophie, not as a whaler, but a Danish merchantman.
In reality, Cochrane noted the similarity between his own brig, Speedy, and a Danish brig that often traveled the Italian coast. As the Danes were neutral, it sailed mostly unmolested by either side. Cochrane repainted Speedy to resemble the Danish vessel, took on a Danish quartermaster, and obtained a Danish flag and suitable uniform.
When surprised by a Spanish frigate, Cochrane installed his Danish quartermaster as captain and hoisted the Danish flag. Although the Spaniards spoke no Danish and the pseudo-captain spoke no Spanish, he was able to get across that the ship was a Danish merchant who had just sailed out of Algiers (where an outbreak of plague was raging). The Spanish ship declined to search the ship for contraband and beat a hasty retreat.
In the battle known as "The Action of 6 May, 1801", Cochrane was again facing a Spanish warship, a xebec-frigate named Gamo, a faster ship than Speedy. Unable to run, Cochrane hoisted American colors, confusing the Spanish long enough for Speedy to close in. Speedy shorter then Gamo such that the latter couldn't depress her guns enough. Cochrane quickly lowered the Stars and Stripes, hoisted the Union Jack, and opened fire. In the ensuing battle, Cochrane captured the much larger vessel.
The general rule seems to have been whatever you can get away with as long as you don't actually open fire under false colors.
Cochrane: The Real Master and Commander, by David Cordingly
There was a very similar question about a month ago answered by u/The_Chieftain_WG.
The correct term for what you're describing is not really rules of engagement, which are the internal policies of a military for using force. Rather, laws and customs of war or law of armed conflict (which nowadays are considered a branch of international humanitarian law) refer to the international norms governing the conduct of warfare. Rules of engagement should implement the laws and customs of war. But another party would complain about a violation of the law and customs of war, not a violation of the rules of engagement.
As discussed in the answer to the other question and by u/RonPossible, disguising a warship as a merchant ship or even as an enemy warship has long been considered an acceptable ruse de guerre.