Actually a fair number could provide longitudinal trim. SE5a is one of the first to make it to ROF that should be able to do so.
There is a worm-gear that raises the front spar of the horizontal stabiliser (the elevator itself remains free-floating, unless 'held' by the pilot, but the required elevator trim force can be reduced to zero by this means).
This makes it more similar to the Bf109 trim, than that fitted to eg the Hurricane or Spitfire (or most other WW2 fighters)
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