Working model, scale 1:12, of twin-cylinder steam driven double trunk screw engines, as extensively used for screw propulsion on the HMS 'Minotaur' and 'Northumberland' (1865-1868), construction patented, and model made by John Penn and Sons in 1845, mounted on ships hull model showing arrangement of engine mounting points made by South Kensington Museum (Workshops), in glass case on table stand (see note). A Trunk Engine was originally developed to reduce engine height while maintaining a long stroke. The long stroke meant that the engine retained greater power while a low profile was curcial for placing the engine as deep in the ship as possible. This depth was ideally below the waterline in the event of enemy action.

Contemporary builders' model of the trunk engines of HMS 'Northumberland', 1868 and HMS 'Minotaur', 1867 Scale 1;12. These engines employ the 'double trunk' layout patented by John Penn the younger (1805-1878)