Australian Army Museum of Western Australia > Records

World War 2, Western Australia, Rottnest Island, Coast Artillery Instrumentation, Fortress Plotter No 1 Mk 1

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Coast Artillery Fire Control - Target and Projectile Coincidence

Overview

Fortress Plotter No 1 Mk 1 – The Plotting Table is intended to be used as a range finder and with the information obtained from it, the target location can be transmitted to the Battery Plotting Rooms. This would occur when conditions made use of battery Depression Range Finders unreliable.
The plotter was a D shaped table with a radius of 1.98 metres (6.5 feet) gridded in the coordinates of the fortress area. Along its straight side, pivot points were fixed in the relevant position of each Fortress Observation Post. Two horizontal bearing arms were attached to the relevant Fortress Observation Post pivots allowing the arms to traverse on a runner track on the curved side of the table.

Details

Registration number

cwa-org-32-54-521

Inscriptions and markings

The runner track was graduated in coloured bearings, one for each of the Fortress Observation Posts. The Plotting Tables were thus customised and unique to each location. (Bickley Point was #38) In operation the bearing arms were positioned based on the information supplied by the Observation Posts with the target location being the point of intersection. A running plot traced the movement of the target enabling course and speed to be determined and communicated to the Coordinate Converter in the Battery Plotting Room.

Contextual Information

This entry is based on research, documentation and technical drawings prepared by John Mercer during many years as a leading member of the Rottnest Island Military Restoration Committee and the Defence Heritage Interpretation Plan Group.

Australian Army Museum of Western Australia

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