It could easily be seen by ships in the Firth of Forth and was a useful safeguard if prevailing winds carried the sound of the gunfire the wrong way.
The ships could never hear the gunfire.
mnli hypothesis: The ships could never hear the gunfire. premise: It could easily be seen by ships in the Firth of Forth and was a useful safeguard if prevailing winds carried the sound of the gunfire the wrong way.