Found this passage in the book Patrick O'Brian's Navy (p. 57)

In the era of fighting sail there was an unspoken convention that line-of-battle ships did not fire on frigates during any fleet action unless the frigate opened fire first. [...] This convention applied only in a general fleet engagement, so a frigate caught alone while cruising, for example, was "fair game" for any larger ship.

I'm curious about this convention. How did it develop and what was its intended purpose? Naturally, in a battle, any enemy should be "fair game", but if this convention was observed, it must have had a clear benefit to everyone.

  • 2
    Not really an answer, but this thing works two ways: When the ships-of-the-line clash, and the frigates don't fire, the enemy ships-of-the-line are the higher priority target. Why would you waste broadsides at a frigate over there when the enemy line is firing at you right here and you stand a chance of removing enemy guns from the battle, instead of adding them?
    – DevSolar
    Apr 5, 2016 at 15:00

2 Answers 2


In age-of-sail fleet actions, the primary use of frigates (and smaller vessels) was to relay messages (usually in the form of flag signals) between the flagships and the rest of the fleet. They usually set themselves some distance from the main 'line' of battle where they could see and be seen by the ships of the line.

A secondary purpose was to act as tugs and rescue vessels for the ships of the line when they were dismasted or even sinking during or after the battle. In the case of a sinking or burning vessel, it was not unknown for frigates to act to save the sailors regardless of whose side they were on (as they were then considered non-combatants). As well as saving their own ships, it was also possible for them to take possession of enemy prizes when their ships of the line were unable to do so.

Given these roles, it's not surprising that the unwritten rule of not firing on the smaller ships arose. It was a great benefit for both sides to have ongoing signalling through the battle and, likewise, useful for both sides to have a source of rescue available if needed.

It should be noted that throughout the Napoleonic Wars (which edged towards total warfare), as frigates had grown considerably larger and more powerful, observance of this rule was starting to wane considerably.

As frigates came to be seen as players rather than onlookers in a fleet engagement, the old conventions surrounding their immunity also broke down; indeed by the 1790s it was already a custom more honoured in the breach than in the observance.

Source: Frigates of the Napoleonic Wars, R. Gardner (Chatham, 2006), pg 159-162.

  • 3
    Very good answer, thanks. Will probably accept your answer after waiting around for a little bit.
    – user69715
    Apr 3, 2016 at 20:02
  • 11
    @Utku As noted in the answer, once a sailor was leaving a sinking ship (or in the water), he was no longer a combatant but simply a fellow sailor in need of rescue from the sea - they would (obviously) be treated as prisoners of war once aboard. AFAIK, there are no examples of sailors taking up arms against their rescuers when saved in this manner.
    – Steve Bird
    Apr 5, 2016 at 11:03
  • 15
    @Utku: The same as why medics would help soldiers regardless of nationality, or you would not fire at soldiers who had surrendered: In the end, once he's stopped shooting at you, an enemy is just another human being, wounded, in pain, and in danger of perishing. You would want them to do the same for you if the roles were reversed. And your average soldier isn't a stone-cold killer either...
    – DevSolar
    Apr 5, 2016 at 14:57
  • 3
    Actually not ONLY the same. IIRC it was not really common for sailors to be able to swim (end even if - swimming long enough to get saved). As the custom to save sailors in the water was done in BOTH directions, it served a purpose as insurance on your own life to save your enemies.
    – TomTom
    Apr 5, 2016 at 23:04
  • 2
    The custom of saving sailors from any side, just like that of taking prisoners-of-war on land, survived into WW2 although it was impaired by the inability of submarines to take prisoners. It's been badly eroded in recent years, e.g. Italy making it illegal to rescue refugees from the sea.
    – pjc50
    Oct 3, 2018 at 11:17

It is probably smart to use your ammunition only on ships in combat, firing at non-combatant ships has two disadvantages, first they might be inclined to join and secondly you should prioritize firing at ships that attack you.

  • 1
    This answer would be improved by references - particularly the implication that Frigates were non-combatants.
    – MCW
    Apr 5, 2016 at 11:44
  • 3
    When this "immunity" rule first came into existence, the supporting vessels were significantly smaller than the ships of the line. Consequently, the small ships lacked the firepower to significantly change the balance of the battle, so they weren't worth the ammo and they were harder to hit (being smaller and further away). As noted in my answer, the rule fell from use as frigates got closer to the ships of the line in terms of size and firepower, and their ability to directly alter the course of the battle increased.
    – Steve Bird
    Apr 5, 2016 at 12:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.