Guthrie rolling bridge

It was commonly installed as the access across the narrow steep sided ditches characteristic of the polygonal forts of this era.

Running the bridge out is effected by pushing it along its rails until the outer two wheels are at the edge of the granite sill of the ditch.

At the same time the outer ends are pulled from the lip of the granite slab, the wheels rolling down the sprung metal guides.

Once the lifting arms are in the fully retracted position the centre wheels are on top of the metal trays and the axles disengage from the cups.

The subject was considered at a meeting of the Ordnance Council held at War Office 9/ 7/69, and it was resolved to recommend the grant of 100l.

A sum of 100l was inserted in the Army Estimates for 1870-71 as a reward to Mr. Guthrie; sanctioned by Parliament; and claim allowed, 27/07/70[3] Bridges of this type were fitted to the forts of the Portsdown Hill line at Portsmouth.