Used in:

5.0-inch Rocket Head Mk 10 (High Capacity)

5.0-inch Rocket Head Mk 12 (High Capacity)

5.0-inch Rocket Head Mk 13 (High Capacity)

Overall dimensions and weight of fuze:

Length

Diameter (maximum)

Body threads

Weight

Applicable specification: OS 3303

General arrangement drawing:

422326 (Mod 3)

562339 (Mod 4)

Sketch list of drawnings & specs:

109113 (Mod 3)

165551 (Mod 4)

Explosive components:

A sensitive stab type Detonator Mk 25 (lead azide priming mixture and lead azide) lo-cated in the head of the fuze.

A Relay Detonator Mk 29 (lead azide) located in a bakelite detonator holder in the body of the fuze.

General. Fuze Mk 30 was originally developed for use as a projectile nose fuze; how-ever, Fuze Mk 30 Mod 3 or Mod 4 has been adopted for use with the spin-stabilized rock-et. Fuze Mk 30 is a centrifugal arming, impact firing, nose fuze and is completely armed when the rotational velocity of the rocket reaches the range of 1500 to 2000 rpm. The fuze is designed to fire superquick on impact with suitable targets. Fuze Mk 30 Mods 3 and 4 differ from Fuzes Mk 30 Mods 0, 1, and 2 (obsolete) by the addition of a safety disc between the exhaust end of the flash tube and the relay detonator to prevent oc-casional initiation of the relay detonator by the flash from accidental firing of the nose detonator when the fuze is unarmed. Fuzes Mk 30 Mods 0, 1, 2, and 3 have a plastic ogive whereas Fuze Mk 30 Mod 4 has a drawn steel ogive. Fuze Mk 30 is always used in conjunction with an auxiliary detonating fuze to assure the complete initiation of the main explosive charge of the rocket head and to provide additional safety.

Figure 1 – Fuze Mk 30 Mod 3 (Point Detonating), External View, Actual Size (approximately).

Figure 2 – Fuze Mk 30 Mod 4 (Point Detonating), External View, Actual Size (approximately).

Use. Fuze Mk 30 Mods 3 or 4 is used in the 5.0-inch High Capacity Spin Stabilized Surface Rockets (Complete Rounds) Mk 10 Mod 0, Mk 13 Mod 0, and Mk 16 Mod 0 (see OP 1415). The above rockets are used for bombardment puposes.

Functioning mechanism. The fuze consists of four basic units, namely: (1) Body as-sembly, (2) Plastic or steel ogive, (3) Flash tube, and (4) Head assembly.

The body, located at the base end of the fuze, is threaded to engage the fuze adap-ter of the rocket head and houses the centrifugally actuated interrupter assembly, the safety disc, the relay detonator, the detonator holder, and the bottom closing screw as-sembly

The interrupter assembly consist of a solid cylindrical metal interrupter, a cylindrical setting sleeve with an eccentric bored interrupter guide well, and an interrupter spring bearing against the spring cup and the bottom of the interrupter guide well. The assemb-ly is held in position with a tension spring and setting sleeve retainer.

The interrupter bears against the spring cup and extends slightly into the guide well of the setting sleeve. In the OFF–OFF position the interrupter rests against a narrow shoul-der formed by a shallow counterbore in the guide well and is locked in place, blocking the flash channel. When the setting sleeve is rotated through 90 degrees of the ON–SQ posi-tion, the interrupter is coaxially aligned with the guide well and is free to move out of the flash channel against the spring and into the guide well when centirfugal force acts upon the interrupter.

The flash tube, threaded at each end, serves a double purpose in transmitting the flash from the initiating detonator to the relay detonator and in providing a means of as-sembling and securing the body, ogive, and head. One end of the flash tube is screwed into the body until seated, the ogive is then slipped over the body, and the head is screwed down on the forward end of the flash tube until the head bears against the lock washer on the plastic or steel ogive.

The head houses a thin metal closing disc, a firing pin, a light metal firing pin support, and a stab type detonator with its retaining screw. The stab type detonator is fired when sufficient force applied at the nose of the fuze deforms the closing disc and drives the pointed firing pin back to collapse the firing pin support and to penetrate the primer mixture.

Figure 3 – Fuze Mk 30 Mod 0 (Point Detonating), Cross Section View,
Unarmed Position

Arming. Prior to firing, the setting sleeve is rotated to the ON-SQ position. When the rocket is fired and it reaches a rotational velocity within the range of 1500 to 2000 rpm, which represents approximately 15 to 25 feet of travel in the rounds in which it is used, the interrupter moves out against the interrupter spring and clears the flash channel thus arming the fuze. The rotational velocity or spin rate remain sufficiently high to maintain the armed condition until after impact.

Firing. Firing is initiated by impact with any material offering sufficient resistance such as wood, metal, ground, or water. Under the force of impact the closing disc is de-formed and the pointed firing pin is driven back to collapse the firing pin support and to penetrate the pimer mixture, thus initiating the stab type detonator. The flash from the stab type detonator passes through the flash tube and initiates the relay detonator which fortifies the action required to initiate the auxiliary detonatong fuze detonator, which in turn initiates the auxiliary detonating fuze lead-ins, booster charge, and finally the main explosive charge of the rocket load.

Figure 4 – Fuze Mk 30 Mod 3 (Point Detonating), Partial Cross Section View,
Armed Position

Acceptance test data. Sample fuzes chosen at random from each production lot are subjected to routine safety tests and ballsitic test when fired in gun ammunition in ac-cordance with table 1.

For every twentieth lot eight ground impacts are substituted for the water impacts, and fired in 6"/47 DP projectiles. If these are not availabe, 5"/54 or 4"/50 HC projectiles are used. Angles of fall and striking velocities should duplicate short and long range bom-bardment by the same type of gun in service. In every twentieth lot ½ inch mild steel is substituted for the wood target.

No prematures are allowable. Two duds out of all fuzes fired from each lot are allow-ed, and in addition to the two duds not more than one failure to give instantaneous action is allowed. Instantaneous action is defined as the destruction of the wood or steel target by blast and fragments of the projectile acting on the side towards the gun, or in case of water or ground impacts the apparent burst of the projectile on contact with the ground or water without intermediate ricochet.

Ballistic tests should be frequently conducted in guns in the last third of their normal life.

Sensitivity limits. The fuze will detonate on ½ inch wood, or water, or ground im-pacts at nonricochet angles. In the case of ground impacts, functioning is reliable at angles of fall of eight degrees or greater; for water impacts, functioning is reliable in rockets at angles of fall of twelve degrees or greater.

Table 1

Caliber

Rounds

Velocity

Material

Obliquity

Range

3"/50

2700 f/s

1" wood

400'

3"/50

1400 f/s

1" wood

400'

4"/50

2900 f/s

1" wood

400'

4"/50

1400 f/s

1" wood

400'

3"/50 to 6"/47 DP*

8

Service

Water impact

Various

*Any caliber normally assembled with Fuze Mk 30 is used. 5"/54 caliber and 6"/47 dual purpose is to be used whenever practicable. Gun elevation must exced eight degrees, and at least two fuzes from each lot are fired at proof (generally 15 percent greater than service pressure) or near proof, preferable in a 3"/50 caliber gun.

Detonator safety. The stab type detonator assembly is always in line, therefore suf-ficient impact on the nose of the fuze will cause crushing of the firing pin support and permit the firing pin to penetrate the primer mixture. In the event the stab type detona-tor does fire (should the fuze be subjected to impact during rough handling), the inter-rupter will block the passage of the flash to the relay detonator. However, to increase the safety in the event that some flash gets around the interrupter, a thin aluminum safety disc (0.001 inch thick) blocks this flash from initiating the relay detonator. Comp-lete arming can only be accomplished after a sustained centrifugal force of the magni-tude attained in flight when the setting sleeve is set on the ON-SQ position. Under such conditions, the interrupter moves out of the flash channel, and the safety disc does not appreciably impede the functioning of the detonating train.

Additional safety of the round is brought about by the use of an Auxiliary Detonating Fuze which has both lead-in and detonator out of line and requires a rotational velocity greater than the minimum arming spin of the nose fuze to become fully armed.

During shipping and stowage. Fuze samples from production lots are subjected to rough handling test which are considered to be more severe than conditions encountered in normal stowage and shipping. Failure of the samples to pass the tests is cause for re-jection of the lot.

Should the stab type detonator function while the fuze is in the unarmed condition, the locked interrupter and safety disc prevent initiation of the balance of the explosive train.

General. In the event that an unfired fuze is damaged because of rough handling, an examination of the condition of the closing disc in the head assembly will determine the method of disposal of the fuze. If upon examination it is found that the closing disc has been deformed or broken, there is the possibility that either the stab type detonator has been fired and has rendered the fuze inactive or that the detonator has merely been pierced and has not been fired. In either case the fuzed rocket head, or the rocket fuze if not assembled into a rocket head should be disposed of by gently lowering into deep water or by Explosive Ordnance Disposal Personnel in accordance with existing instruct-ions. If upon examination, it is found that the closing disc has not been damaged and the setting sleeve is set to the OFF-OFF position, the fuze may be considered safe to hand-le, or if the closing disc is not damaged in any manner and the setting sleeve has been set to ON-SQ position, the fuze may be rendered safe for handling by rotating the sett-ing sleeve to the OFF-OFF position.

Disassembly. Disassembly of this fuze is not permitted except at authorized activi-ties when directed by the Bureau of Ordnance.

1. Remove the nose shipping plug from the rocket head. Inspect the threads and the interior of the rocket head nose fuze cavity. Clean if necessary. Be certain that the auxi-liary detonating fuze is present in the rocket head.

2. Remove Fuze Mk 30 Mods 3 or 4 from the container and examine it for damage and setting.

3. Install the fuze into the rocket head and be certain that it seats properly.

4. The fuze is shipped with the setting sleeve set to OFF-OFF position. Before firing, set the setting sleeve to ON-SQ position by inserting a screwdriver of similar tool into the slot on the setting sleeve and turning it so that the slot aligns with the ON-SQ let-tering on the ogive.

Removal from round. The fuze may be removed from the rocket head with the pro-per fuze wrench and returned to the shipping container. The closed shipping container can should in turn be sealed with adhesive tape along the broken surface. Before removal of the fuze from the round, the setting sleeve shall be returned to the OFF-OFF position. The shipping plug with gasket must be replaced into the rocket head after the fuze is re-moved.

Packing. Fuze Mk 30 Mods 3 or 4 issued in an individual hermetically sealed metal can. Twenty-four individual cans are packed in a wood box 25½ inches by 16½ inches which represents a total of 1.5 cu. ft. and a total weight of 65 pounds.

Marking. The lettering OFF-OFF and ON-SQ is stamped on the ogive. These markings are at right angles to each other and are spaced around the hole for setting screw with the fuze nose end up. ON-SQ is positioned vertically and OFF-OFF horizonatally.

The fuze is marked or stamped with the letters PDF, the mark, mod, and lot number, the manufacturer's initials or symbol, the initials or symbol of the loading facility, the month and year of the loading, the anchor stamp, and the inspector's initials.