Deck needs sailors joining a party (5)
I believe the answer is:
adorn
'deck' is the definition.
(I've seen this before)
'sailors joining a party' is the wordplay.
'sailors' becomes 'RN' (abbreviation for Royal Navy).
'joining' means one lot of letters go next to another.
'party' becomes 'do' (do is a kind of party).
'a'+'do'='ado'
'rn' put after 'ado' is 'ADORN'.
'needs' acts as a link.
(Other definitions for adorn that I've seen before include "Embellish, decorate" , "dress" , "Bedeck" , "Attire" , "Deck" .)