Warship crew's heading in to press youngster (8)
I believe the answer is:
ironclad
'warship' is the definition.
(19th century armoured warship)
'crew's heading in to press youngster' is the wordplay.
'crew's heading' becomes 'c' (I can't justify this - if you can you should believe this answer much more).
'in' indicates putting letters inside.
'to press' becomes 'iron' (ironing is a kind of pressing).
'youngster' becomes 'lad' (a young boy).
'iron'+'lad'='ironlad'
'c' put into 'ironlad' is 'IRONCLAD'.
Can you help me to learn more?
(Other definitions for ironclad that I've seen before include "in the mail" , "Absolutely determined" , "Old cairn with metal protection" , "Protected as by armour - say an alibi" , "C 19 armoured warship" .)