Model 2, slightly modified over original and Model 1. 5.511” long. Brass, steel, phosphor-bronze diaphragm. HIR (“hydrostatic-arming, impact-firing rocket”) fuzes were for shipboard rockets (7.2” rocket, Mk1, 2, 4) and for aircraft rockets for retro-bombing (rockets fired rearward from low-flying aircraft) (7.2” rocket, Mk3, 5). They originated at Caltech and were placed in limited production. 25,000 were produced then abandoned in favor of the smaller MK140. Cutaway model.
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