### Clue: Tower Bridge initially smothered in butter, half of tuna on top! (7)
### Answer: TUGBOAT 
 ### Explanation: Definition: Tower
  TU(half of the letters of "tuna") ***placed above***(on top, in a down clue) [B(initial letter,initially of "Bridge") **contained in**(smothered in) GOAT(an animal that likes to butt,a butter)]. 
Answer: A tower (and sometimes pusher) of ships.  Nice misdirection; another favourite.