Operational instruments of the Royal Observer Corps

This sub article lists and describes the instruments used by the ROC in their nuclear detection and reporting role during the Cold War period.

The Bomb Power Indicator or BPI consisted of a peak overpressure gauge with a dial that would register when the pressure wave from a nuclear explosion passed over the post.

This meter suffered from a number of disadvantages: it required three different types of batteries, of which two were obsolete and had to be manufactured to special order, the circuit included a single electrometer valve or tube.

For the first time it was possible to operate the unit from within the Monitoring Post or Group HQ using an external Geiger Muller Probe connected via coaxial cable and mounted to a telescopic rod and protected on the surface by a polycarbonate dome.

It gave more accurate readings and used standard 'C' cell torch batteries that lasted many times longer, up to 400 hours of operation.

The compact and robust instruments were housed in sturdy orange coloured polycarbonate cases and had clear liquid crystal displays.

The PDRM82(F) could also be operated from within the Monitoring Post or Group HQ as before, using an external Geiger Muller Probe connected via coaxial cable.

The compact and robust instruments were housed in sturdy orange coloured polycarbonate cases and had clear liquid crystal displays.

ROC post observers in an underground monitoring post during a Cold War training exercise. The BPI dial can be seen in the background with a teletalk, FSM radiac instrument and a WB400 receiver on the desk.
AWDREY Computer.
Bomb Power Indicator with ‘Kilopascal’ overlay. This was added in the 1970s to cover the original P.S.I scale which had been superseded.
Internal view showing the ‘North Cassette’ which would have held the photosensitive paper.
Exterior profile of GZI with two of the four ‘pinholes’ visible.
RSM No.2
The ‘ROC Fixed Survey Meter’. Manufactured by AVO and introduced in the 1950s.
Polycarbonate Dome which was fitted on the surface and held the Fixed Survey Meter Geiger Muller Probe inside. This unit remained unchanged when the PDRM82(F) replaced the FSM.
Plessey PDRM82(F)
PDRM82F Geiger Muller Probe on its mounting bracket, fitted to the Telescopic Probe Rod.
Radiac Survey Meter, Lightweight, MkVI
Plessey PDRM82.
Early hand wound unit. Charging Unit No.1
Later battery unit. EAL N.105A