3a. Gilbert's modern model in brass
MAJOR-GENERAL
24a. Something badly done has friend appearing for trial
COCK-UP
27a. Taking care always to be in the right gear
DRESSY
4d. Support of knights for series of contests?
CHAMPIONSHIP
17d. Crown left in ship's tender
PINNACLE
18d. Hollow warning of schoolboys to sailors
CAVERN
Parses for the above please.