Type P4 No. 28014 B aeronautical compass
Date1946
Object number00029519
NameCompass
MediumMetal, plastic, liquid, radioactive material
DimensionsOverall: 95 x 165 mm, 2.65 kg
ClassificationsTools and equipment
Credit LineANMM Collection Gift from the Estate of WIlliam Cross
Historyhttp://compassmuseum.com/aero/aero.htm
The P4 was a mid-1930s compass and was used in “large” aeroplanes, including the Hawker Hart, Sunderland and early four-engined bombers. It was replaced by the P10, which was identical in size but had four cross hairs rather than two. Some P4's were modified with four cross hairs as P4A. It was the P10 that would have been fitted to the Lancaster rather than the earlier P4, but I have no doubt that P4's were also used when the need arose
CAUTION - RADIATION HAZARD
The cardinals (N-E-S-W) and the 10-deg. markings on the compasses were made of a radioactive compound (radium and zinc sulfide/copper) which is still "hot" although the paint is no longer visible in the dark. In 50 cm (1 1/2 ft) distance, the gamma radiation measured is 0.35 µSv/hr (microsieverts/hour). The natural background radiation is about 0.10 µSv/h. The threshold for hazardous radiation is 0.30, this means that this instrument is not dangerous if always kept at this safe distance from the body (10 ft).
1890s - 1950s
