Wiktionary
n. 1 (context nautical English) (plural of narrow sea English) 2 (context nautical legal UK English) Those seas (bodies of ocean water) which surround the British Isles, especially the English Channel.
Usage examples of "narrow seas".
SIX MONTHS LATER A MAN LED AN INVASION FORCE across the Narrow Seas.
And folks are asking, why does King William keep our best commander locked up on a ridiculous pretext, when a great campaign is under way on the other side of the Narrow Seas?
There was every reason to fear such an engagement in these narrow seas, in which pirates could ply their trade without risk.
The waves were bounding about us with that short and angry leap peculiar, in tempestuous weather, to the narrow seas between England and France.
If an ocean of similar shape had existed on Earth, it would have been a bigger Arctic Ocean, covering most of Russia, Canada, Alaska, Greenland, and Scandinavia, and then making two deeper incursions farther south, narrow seas that extended all the way to the equator.
Sea power made its influence felt all over the wide oceans, but it was in the narrow seas, at the focal points, that the decisive moments occurred.