University club housing old submarine (1-4)
I believe the answer is:
u-boat
'submarine' is the definition.
(synonyms)
'university club housing old' is the wordplay.
'university' becomes 'u'.
'club' becomes 'bat' (as in sporting equipment).
'housing' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'bat' placed around 'o' is 'boat'.
'u'+'boat'='U-BOAT'
(Other definitions for u-boat that I've seen before include "Take pool exercise" , "Submersible warship of WWII" , "German World War One or World War Two submarine" , "German WW 2 sub" , "German submarine of WW2" .)