Abstract: Disclosed is an improved underwater half-second pyrotechnic delay device ing an elongated tubular housing with a pair of holes for respectively threading suitable detonating cords through each end thereof. In operational burning series within said tubular housing are a plurality of lead sheathed protected explosives, a resilient pressure attenuating disc, a metallic capsule containing a calibrated delayed burning composition of 2/98B-Pb.sub.3 O.sub.4 having such geometrical configuration as to effect burning therealong for one-half second with considerable accuract, and another series of lead sheath protected explosives, a base charge, an explosive cord, and an end plug. An appropriate number of crimps are made along said tubular housing for holding the aforesaid elements in their proper places therein. Seals are employed at each end of said housing to make it watertight.