British Cluster Projectile, 500 lb, No. 6 Mk 1, No. 6 Mk 2
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 directions. 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 tensioning straps. A shear wire passes through the retaining bar and a bridge on 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 outer 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 retaining 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 dowels 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.
The tail unit consists of a tail cone with an approximately hexagonal 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 bearings, which has a fork at its inner end and an arming vane at its outer end. The safety 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.
A British type suspension lug is fitted to the top beam of the cluster, and tapped holes are provided for fitting American type lugs.
The Cluster Mk I contains 90 4-lb. Smoke Bombs Mk III. The Cluster Mk II is identical to the Mk I, except that it contains 90 4-lb. Smoke Bombs Mk II** or Mk IV.
If the smoke composition used in the 4-lb. smoke bombs gets wet, and especially if wetted by sea water, it is liable to spontaneous combustion through chemical action.
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