Weapon for which gunners need a landing-place (6)
I believe the answer is:
rapier
'weapon' is the definition.
(I know that rapier is a type of sword)
'gunners need a landing-place' is the wordplay.
'gunners' becomes 'RA' (Royal Artillery).
'need' says to put letters next to each other.
'a landing place' becomes 'pier' (pier is a kind of landing place).
'ra'+'pier'='RAPIER'
'for which' is the link.
(Other definitions for rapier that I've seen before include "fencing equipment" , "Narrow sword with two-edged blade" , "Thin sharp sword" , "A thin double-edged sword" , "Sword for thrusting" .)