Smoke 4-lb. Mks I, II, and IV (Service)

Body Construction: The bomb consists of a cylindrical metal body closed at both ends and containing a smoke composition. At the tail end of the bomb is a baffle plate secured to the body and provided with a smoke emission hole covered by a strip of pri-med fabric held in place by two strips of adhesive tape. Beneath the baffle plate is an ig-niter pellet secured to a strawboard washer. The hole in the washer is filled with match composition which contacts the igniter pellet. The igniter pellet is set in the smoke com-position.

Above the baffle plate is a lid secured to the bomb body and provided with a screw-threaded fuze adapter. The Fuze No. 859 Mk I is screwed and cemented into the fuze adapter.

Functioning: When the bomb is released from the Small Bomb Container, the safety cap of the fuze is drawn off by the section of air resistance on the fabric drogue. The lead sleeve on the webbing tape attached to the safety pin causes the free end of the tape to clear the waisted portion of the fuze body and be caught in the air stream, thus withdrawing the safety pin. The fuze is now armed, with the lead ball and striker held away from the detonator by the creep spring alone.

On impact with the target, the fuze functions. The flash from the detonator passes through the flash hole in the fuze body and fires the primed cambric strip, which in turn ignites the match composition. The match composition fires the igniter pellet, and this ig-nites the smoke composition.

The smoke generated passes through the smoke-emission hole in the baffle plate and builds up pressure beneath the lid, thus bursting the adhesive tape covering the small smoke-emission hole in the lid and permitting the smoke to escape into the air. After a short period of time the heat evolved in the bomb melts the solder securing the lid to the bomb body, and the pressure of the smoke then forces off the lid.

Suspension: These bombs are designed to be carried either in the 250-lb. Small Bomb Container, ot the 500-lb. Cluster Projectile No. 6 Mk I, Smoke. In the former, the bombs are packed 14 in a metal case, and three cases are placed in the Container. In the lat-ter, 90 bombs are carried in five tiers of 18 bombs each. They are placed end to end lon-gitudinally, with the fuzes pointing in opposite directions in alternate tiers.

Filling: The filling of the bomb consists of a cambric strip primed with S.R.  252, a cambric square primed with sulphurless gunpowder, ¼ lb. smoke composition S.R. 269 (M), and 3¼ lb. smoke composition S.R. 264 A (M).

Remarks: Spontaneous ignition of smoke compositions may result if the filling is wet-ted, especially by sea water. The bombs are dropped from aircraft to produce a smoke screen to cover land operations.

The Bomb Mk II is identical to the Mk I, except that the smoke composition is slower burning. The Bomb Mk IV is similar to the Mk II, except that the closing lid of the bomb body and the igniter pellet are slightly altered.

Figure 46 - Smoke 4-lb. Bomb Mk I