Black and blue tubes in weapons (9)

'weapons' is the definition.
(I've seen this before)

'black and blue tubes' is the wordplay.
'black' becomes 'b' (abbreviation as in pencil classifications).
'and' means one lot of letters go next to another.
'blue' becomes 'low' (both can mean sad).
'tubes' becomes 'pipes' ('pipe' can be a synonym of 'tube').
'b'+'low'+'pipes'='BLOWPIPES'

'in' is the link.