Cluster Projectile 500-lb. No. 6 Mks I and II (Service)

Description: The cluster is hexagonal in cross section and comprises ninety 4-lb. smoke bombs, arranged in five fagots of eighteen bombs each. The bombs are arranged nose-to-tail longitudinally, and in alternate rows the bomb fuzes point in opposite direct-ions. The bombs are held in place by a front end plate and a rear end plate, a top beam and a bottom beam, four side plates, tensioning straps, and a retaining bar. Lateral pins on the retaining bar engage tabs forming part of shoes attached to the ends of the ten-sioning straps. A shear wire passes through the retaining bar and a bridge of the top beam. The four side plates, together with the two beams, completely surround the bomb cluster. A channel secured to the rear end plate supports a fuze adapter, the cuter end of which is closed by a transit plug and leather washer. Inside the adapter is a piston through which is a pin to engage the lower end of a pivoted lever. The fuze adapter and piston are slotted to receive the lever, which is connected at its upper end to the retai-ning bar.

The rear end plate has two dowels for locating the tail in position, and a nut welded to the center of the plate receives one end of a tail tie rod when the tail unit is fitted to the cluster. The front end plate has two dwoels for locating a nose cover in position. A securing bolt is screwed into the center of the nose end plate to receive a fixing nut, when the nose cover is fitted to the cluster.

Tail Constructio: The tail unit consists of a tail cone with an approximately hexago-nal base, and a tail strut secured to the cone by fins. At the base of the tail cone are two holes to fit over the dowels on the rear end plate of the cluster. A tie rod passes through the center of the tail, and one end of this rod is threaded to screw into the central nut on the rear end plate. The other end of the rod is fitted with a tensioning nut for securing the tail to the cluster. The tail unit also has an arming spindle mounted in bearnings, which has a fork at its inner end and an arming vane at its outer end. The safeyt wire, when fitted passes through holes in a bracket, a projection on the support for the arming spindle bearings, and a blade of the arming vane. Two inspection windows in the tail cone are provided to enable the armorer to watch the fork of the arming spindle, when fitting the tail unit.

Functioning: When a cluster projectile fuzed with a Fuze No. 867 is released, safety wire is withdrawn from the tail-unit arming vane and the shear wire of the fuze is broken to release the fuze safety pin. After a period of delay during which the cluster projectile falls freely, the fuze magazine is fired. The products of combustion of the magazine charge force the piston in the fuze adapter against the lower end of the pivoted lever, which is tus rocked about its pivot and exerts a pull on the retaining bar of the cluster. The pull breaks the shear wire passing through the retaining bar, and moves the bar so that its pins disengage the tabs on the shoes attached to the tensioning straps. The straps then fly outwards and the cluster disintegrates, its component parts falling away separately. The individual bombs function on impact.

Suspension: A British type suspension lug is fitted to the top beam of the cluster, and tapped holes are provided for fitting American type lugs.

If the smoke composition used in the 4-lb. smoke bomb gets wet, and especially if wetted by sea water, it is liable to sponatneous combustion through chemical action.

Figure 107 - Cluster Projectile 500-lb. No. 6