Cluster Projectile 750-lb. No. 15 Mk I (Service)

Description: This cluster comprises two fagots of 79 bombs each. The bombs in each fagot are arranged nose-to-tail with their safety plungers inwards so that they are all depressed. The bombs are held in place by a front end plate and a rear end plate, a top beam and a bottom beam, four wooden slats, tensioning straps, and a retaining bar hav-ing lateral pins which engage tabs in the tensioning straps. A shear wire passes through a bridge and the retaining bar at a position near the end plate. A channel serured to the rear end plate supports a fuze adapter, the outer end of which is closed by a transit plug fitted with a leather washer. Inside the adapter is a piston through which is a pin arran-ged to engage the lower end of a pivoted lever. The fuze adapter and the piston are slotted to receive the lever. The upper end of the lever is forked and is connected 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 rear end plate to receive one end of a tail tie rod when the tail unit is fitted to the cluster. A nose cover is fitted to the front end plate to de-crease the drag of the cluster.

Tail Construction: The Tail Unit No. 43 Mk I is a shortened drum-type tail, having a tail cone to which a tail strut is secured by fins. At the base of the tail cone are two ho-les designed to fit over the dowels on the rear end plate of the cluster. The tail unit is fitted with a bearing for an arming spindle so that, if it should ever be required to fuze the cluster with an air armed fuze, a suitable arming spindle with an arming vane could be readily fitted. Two windows, one of which is open, are provided in the tail cone. The open window is provided to that, when the cluster is prepared for use, the fuzing link connected to the pull-percussion mechanism of the Fuze No. 42 Mk IV can be passed through it and be connected to the fuzing unit of the bomb carrier.

Functioning: When a fuzed cluster projectile is released, the fuze functions, and, after a delay during which the cluster projectile falls freely, the fuze magazine charge 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 thus rocked about its pivot and exerts a pull on the retaining bar of the cluster. This causes the retaining bar to break its shear wire and to be moved so that the pins on the bar disengage the taps on the tensioning straps. The straps then fly outwards and the cluster disintegrates, the component parts falling away separately. The individual 4-lb. bombs function on impact.

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

Figure 111 - Cluster Projectile 750-lb. No. 15 Mk I