The NRA Museum holds this First World War example of a SMLE rifle modified for use over a trench parapet.

The unit can be fitted moderately quickly to any SMLE rifle without need of any tools; the parts clamping in place and being tightened with wing-nuts. In this demonstration it is fitted to a Long Lee Enfield 303 bolt action rifle.

It is of a design patented by J.E. Chandler on 17th. September 1915 

The design permits not only the firing of the rifle from a protected position using a remote trigger, but also the actioning of the bolt; there being one lever to rotate the handle to unlock/lock the bolt, and another to draw the bolt open and push it home.

The arrangement therefore allows of the firing of a complete magazine containing ten rounds before any necessity to dismount the rifle from its (probably hidden) position.

Two mirrors enable the operator to see along the sights and aim without exposing themselves.

The main unit is held in place by single clamp on the underside of the butt-stock.
A bowden cable from the remote trigger leads to the rifle’s trigger.

Interestingly, less than a week earlier, on 11th. September, a patent was granted to an applicant named Gérard for a remarkably similar design incorporating a Bowden cable operated remote trigger.