I.B. 30-lb. Type J, Mk I (Servcie)

Fuzing

Color markings

Over-all length

Body diameter

Total weight

Wt. thermite

Burning time

Description: The bomb consists of a cylindrical steel body with a dished steel nose plate having a central spigot welded on, a steel ring welded to the nose plate, and a wooden nose covered by a thin metal cap and secured by screws to the ring. A tail plate is welded, near the other end of the body, and a steel central tube, projecting through the tail plate, is welded to the tail plate and the spigot on the nose plate. A magmesium-alloy striker is screwed to the central tube and retains a detonator holder in position. The striker is supported by a two-armed brass cross which engages the top of the hous-ing. A  spring-loaded safety plunger, contained in a sleeve, projects into the path of the striker. The safety plunger is held in position by a retaining sleeve, which is secured to the parasheet container.

An automatic valve is fitted to the tail plate and has an auto-valve body screwed into a socket welded into the tail plate. A tube extension, screwed into the inner end of the auto-valve body, holds a flexible tube, which extends to within three inches of the bot-tom of the bomb. A jet having its outlet hole pointing vertically out of the tail is screwed into the side of the auto-valve body. The valve chamber houses a spring-loaded piston having a rubber sealing disk at its inner end, which normally seals the central hole in the valve body.

The parasheet is housed in a container held in the tail end of the bomb body by six retaining screws, and its rigging lines are anchored to the container. The container is closed by a loose metal cover held in position by the end plates of the cluster projectile. A safety pin retaining sleeve, secured to the cover, is fitted into a central guide tube in the parasheet container, and houses a spring retainer in which is a compressed spring.

Functioning: As the bomb fall free of the container, the spring in the spring retainer of the parasheet container forces the cover away and releases the safety plunger, thus arming the bomb. The cover is blown aft and withdraws the parasheet. When the para-sheet is fully withdrawn, the drag on the cover breaks the linen threads, so that the cover falls away.

On impact, the striker moves forward, bending the arms of the brass cross, and fires the detonator. The flash from the detonator passes through the paper disk covering the holes in the cellophane washer and ignites the primings in the central tube. The priming ignite the thermite, and this heats the interior of the bomb, thus raising the interal pres-sure. The magnesium-alloy striker housing burns away to afford additional venting to the filling in the central tube. When the pressure has risen to about 300 p.s.i. (pounds per square inch), the piston in the automatic valve is raised and the methane and petrol so-lution passes through the flexible tube, into the valve chamber, through the outlet hole in the jet, and through the hole in the bottom of the parasheet container. As it passes out of the jet, the liquid is ignited by the flame issuing from the vent holes in the striker housing as a result of the burning of the thermite.

Because of the lead weight, the free end of the flexible tube always falls to the lower side of the bomb as it comes to rest, so that almost all of the liquid charging passes out of the bomb through the jet. It emits a flame 15 ft. high and 2 ft. wide.

Suspension: Carried in batches of 14 in Cluster Projectiles, 500-lb., No. 4 Mk I.

Filling: The main filling consists of a solution of methane in 1.3 gallons of petrol. The bomb is filled under pressure, so that the normal filled pressure inside the bomb is from 90 to 110 p.s.i.

Figure 42 –I.B. 30-lb. Type J, Mk I