For 5.0" aircraft rocket (Model 0) and for 11.75 aircraft rocket (Model 1 and 2). Dimensions same as PIR-1. PIR-2 is a modification of PIR-1 by replacement of instantaneous detonator with delay detonator (0.02 second delay). This one appears to be a Model 0. Development was begun in Feb. 1944. 6,000 Model 0's were manufactured by Caltech in April and May 1944, for tests by the navy. After standardization 96,000 Mk146 Model 1 fuzes of Buord were converted by Caltech to Mk157, Model 0 fuzes. This occurred in the period Oct. 1944-March 1945.
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