BOMBS USED IN

ARMED CONDITION

FUZES USED WITH

FUNCTIONING

MAX. BODY DIAMETER

OVERALL LENGTH

COLOR

DESCRIPTION:

The No. 850 Mk bomb fuze is a hydrostatic arming, contact firing bomb fuze specially designed for use in the 250 lb Buoyancy bombs. The fuze itself consists of two port-ions, the upper portion housing the hydrostatic mechanism, the lower portion forming the magazine.

The upper portion of the outer casing houses the actuating head, the head being locked to the casing by a ball lock which is freed on impact with water.

The cylinder is of slightly less diameter than the outer casing, leaving a small annular space between the cylinder wall and the casing. The lower end of the cylinder is in the form of a disc contained in the lower end of the outer casing to which it is soldered. A piston supporting stop, consisting of a metal disc with protrusions on both faces, clamps a rubber washer in position and also supports the cylinder wall and the piston. The upper protrusion of the piston supporting stop is provided with ports which, toget-her with ports formed in the lower end of the cylinder wall, connect the space belo the piston with that between the cylinder wall and the outer casing.

The pistion consists of a metal disc with a central hole into which the lower portion of the piston rod is inserted. This portion of the piston rod has a shoulder at its upper end by which the piston rod is raised when the piston is forced up the cylinder by hy-drostatic pressure. The piston rod, which is hollow, is made in two sections. The upper section of the rod houses the release spindle, to which it is locked by a ball. The lower portion of the piston rod is threaded internally to accommodate a screwed ferrule which houses the upper end of the striker, which is locked to the ferrule by a ball lock. The ferrule is bevelled at its lower end and forms part of a lock to prevent the return of the piston after the fuze has been armed. The lock is formed by a locking ball housed in a concial recess formed in the lower portion of the outer casing. A washer and a distance tube are inserted in the lower portion of the piston rod to support the upper section of the piston rod.

The striker is locked by a ball lock to the screwed ferrule in the lower section of the piston rod and protrudes through the lower end of the ferrule. The lower end of the striker is housed in a blind hole in the spring-loaded shutter of the magazone when the fuze is in the safe position. The firing spring, encased in a sheath, is interposed bet-ween the lower end of the outer casing, and a washer supported on a shoulder formed on the striker.

A collar is screwed to the top of the release spindle and forms a bearing surface for the lower end of the actuating head. The thrust spring is interposed between this collar and the upper portion rod. The actuating head is contained in the upper portion of the outer casing, to which it is locked by a ball lock. The actuating head is bored axially to house a hollow inertia bolt which accommodates a spring-loaded plunger. This plunger is rotained in position by the fuze safety clip which passes through the inertia bolt and the actuating head. A retaining pin prevents ejection of the plunger by its spring when the safety clip is withdrawn.

A light friction spring is fitted ot the actuating head and bears on the inertia bolt; this spring engages in a groove in the inertia bolt when the bolt moves down.

The magazine containing two C.E. pellets is attached to the lower end of the sheath surrounding the firing spring and is arranged so that the fuze can accommodate itself to any tolerance in the length of the central tube and exploder column in the bomb. A spring-loaded shutter carrying a detonator is incorporated in the magazine. The shutter is held in the safey position by the striker, and by a transit pin during storage and tran-sit.

The fuze is retained in position in the bomb by a ring nut situated between the flan-ge on the actuating head and the upper portion of the outer casing. A rubber washer around the lower portion of the outer casing forms a water-tight seating when the fuze is assembled in the fuze pocket of the bomb.

FUNCTIONING:

Bomb Dropped Live:

On release frim the plane, the safety clip on the fuze is removed by the fuze setting control link, allowing the plunger to move up under the action of its spring. The ball in the bore of the actuating head is then free to move into the recess in the bottom of the bore.

On impact of the bomb with the water, the nose attachment and tail break away. The inertia weight in the fuze moves downward, due to the retardation of the bomb in the water, thus releasing the ball lock securing the actuating head the the upper port-ion of the outer case.

When the bomb is submerged, water enters the outer caseing of the fuze through the holes in the upper portion of the outer casing, and flows through the annular space between the outer casing and the cylinder wall. It then enters the cylinder through the ports in the cylinder wall exerts pressure on the lower face of the piston. The piston is thereby raised in the cylinder, taking with it the piston rod assembly.

The striker, being locked to the release spindle, moves upward with the piston, and the washer on the shoulder of the striker compresses the firing spring. The raising of the striker also frees the spring-loaded shutter in the magazine, the shutter moving over to align the detonator with the striker.

The motion of the piston also raises the release spindle and the actuating head, which, being attached to the contact disc of the bomb, raises the contact disc to the limit of its seuring chains. The rainsing of the piston rod frees the ball lock securing it to the release spindle.

The ball in the lower portion of the outer casing moves under the bevelled shoulder on the screwed ferrule and so prevents return of the piston once arming of the fuze has been achieved.

Having descended to its maximum depth the bomb ascends contact disc uppermost, at a speed of 3½ ft/sec under the influence of its buoyancy. Any possibility of the bomb's firing due to water drag on the contact disc is overcome by the thrust spring in the fuze.

On impact with the target during its upward motion, the contact disc is forced down relatively to the bomb, causing the actuating head to move down relatively to the outer casing of the fuze. This in turn causes the release spindle to move down relati-vely to the piston rod, thus freein the ball lock by which the striker is locked to the re-lease spindle. The striker is then forced by its spring into the detonator, initiating the normal explosive train.

If the bomb fails to encounter any obstruction during its upward motion, it will rise to the surface and remain there for approximately ten minutes. After this time sufficient water will have entered through the two sinking holes in the buoyancy chamber to cause the bomb to sink to the bottom.

If the contact disc is depressed during the time that the bomb is floating on the sur-face, the fuze will function and detonate the bomb.

Bomb Dropped Safe:

Provision is made in the fuze for dropping the bomb safe. This necessary to provide for jettisoning the bomb in the event of engine trouble during or shortly after the air-craft takes off from a carrier. Safe dropping is achieved by a ball, accommodated in the bore of the actuating head, which prevents the inertia bolt from moving sufficiently in a downward direction to release the actuating head ball lock.

On release from the plane, the safety clip remains in position on the fuze. On impact with the water, the break-up and removal of the tail may cause the safety clip of the fuze to be withdrawn accidentally. The retardation of the bomb in the water causes the plunger to move downward against the action of its spring, preventing escape of the ball into the recess in the bore of the actuating head. The inertia bolt also moves downward, but it is obstructed by the ball and cannot move sufficiently to release the ball lock securing the actuating head to the upper portion of the outer casing of the fuze. The friction spring in the actuating head falls into the groove in the inertia bolt, thus preventing the actuating head from being lifted by wave motions after the bomb has been dropped "safe", insuring that the bomb remains in the safe condition

REMARKS:

1. No. 850 Mk II: The Mk II fuze differs from the Mk I as follows:

(a) The safety clip is replaced by a cotter pin, which pierces both the plunger and the actuating head.