Used in: 7.2-inch Rocket Head Mk 5 (High Capacity)

Overall dimensions and weight of fuze:

Length

Diameter (maximum)

Body threads

Weight

Applicable specification: OS 2374 (where pertinent)

Outline drawing: 423659

Explosive components:

A sensitive stab type compound Detonator Mk 21 (pom-pom mixture and mercury ful-minate)

Auxiliary booster lead-in (tetryl) 0.11 grams

Booster separator lead-in (tetryl) 0.20 grams

Booster (tetryl) 25.5 grams

General. Fuze Mk 152 is identical with Bomb Fuze AN-Mk 210 except that is has been partially armed fifty turns of the arming vanes and a metal band (fork) is inserted bet-ween the vane carrier and the fuze body to take up the space left by the prearming pro-cess. In addition, the pitch of the vanes has been increased to 40 degrees in contrast to the pitch of the vanes on the AN-Mk 219 of 18 degrees. The fuze is air arming, and its functioning is instantaneous on impact.

Use. Fuze Mk 152 is used in the 7.2-inch High Capacity Fin Stabilized Surface Rockets (Complete Rounds) Mk 1 Mod 0 and Mod 1 (see OP 1415). The complete round is used for demolition purposes in the destruction of beach obstacles.

Functioning mechanism. The vane carrier is unlocked from the striker flange by withdrawal of the arming wire. The vane carrier then rotates by action of the airstream on the vane driving the reduction gearing. The reduction gearing reduces the motion so that 23 turns of the vane carrier are necessary to produce one revolution of the shaft. The gearing is so arranged that the lower gear carrier engages the slot of the inner slee-ve. The upper gear, therefore, takes up the rotation and advances the central shaft on its threads until stopped by the shoulder on the saft screw. At about this instant the lug on the lower gear carrier is disengaged from the slot in the sleeve, allowing the lower gear and carrier to rotate. As the rotation of the shaft and upper gear is stopped, the motion is transferred to the lower gear and carrier which rotate approximately 345 de-grees thereby bringing into alignment the firing pin extension, firing pin, and detonator with the booster lead. As this rotation is completed, a locking detent engages the lower gear carrier to maintain proper alignment of the explosive train.

Figure 20 – Nose Fuze Mk 152, Cross Section View,
Armed Position

Arming. The Fuze Mk 152 arms in two stages. During the first stage, the upper gear is free to rotate adn the lower gear, being attached to the hammer carrier which in turn is locked by the inner sleeve, is held stationary. During the second stage, the hammer carrier has risen to clear the inner sleeve and the lower gear is free to rotate while the upper gear is held stationary as it is attached to the arming shaft which was threaded up until it locked against the shaft extension nut.

First stage. As the rocket is launched, the arming wire is withdrawn and the vanes are free to rotate. Through the system of reduction gears, the upper gear rotates to thread the arming shaft up until the head of the screw on the shaft locks against the shaft extension nut. A collar on the shaft lifts the hammer carrier and the entire arming assembly. Simultaneously with the locking of the arming shaft and the upper gear, the hammer carrier clears the inner shaft to free the lower gear.

Second stage. The lower gear and hammer carrier are rotated in a counterclockwise direction. The aligning lug on the hammer carrier engages the firing pin carrier, lining up the firing pin extension with the firing pin. Further rotation causes the firing pin carrier to engage the detonator carrier, lining the firing pin up with the detonator. The hammer carrier, firing pin carrier, and detonator carrier continue to rotate until the lip on the de-tonator carrier engages the inner sleeve. Simultaneously, the spring-loaded detent in the striker snaps into a recess in the hammer carrier, thus locking the firing train components in an armed position. Since the upper and lower gears are both locked, the two copper pins securing the lower gear to the hammer carrier are sheared and the vanes rotate freely. (If the air speed is less than 300 mph, the air pressure will not be sufficient to shear the pins and the vanes will merely cease rotating.) The fuze is armed after approx-imately 100 revolutions of the arming vane.

Firing. After the above actions the fuze is fully armed. On impact, the entire upper asssembly of the fuze is forced inward. The shear wire in the arming shaft is cut as the upper part of the shaft telescopes into the lower part and the shear wire through the firing pin is cut as the firing pin extension forces the firing pin into the detonator. The detonator sets off the auxiliary booster lead-in, booster lead-in, booster, and man charge successively.

Acceptance test data. Since Fuze Mk 152 is a conversion of loaded Bomb Fuzes AN-Mk 219, acceptance tests were previously accomplished on the fuze as an AN-Mk 219. Acceptance tests in rockets were not accomplished.

Sensitivity limits. Fuze Mk 152, after arming, will detonate the rocket head instant-aneously on impact with water or denser medium.

Detonator safety. Fuze Mk 152 Mod 0 is detonator safe. The detonator is out of alignment with the booster lead-in, the firing pin is out of alignment with the detonator and the firing pin extension is not aligned with the firing pin. If the detonator should function prematurely the gases would expand to the space above and would be dissipa-ted away from the explosive components.

During shipping and stowage. A safety pin locks the vane and prevents rotation. Fuzes Mk 152 Mod 0 are packed and the shipping containers marked in such a manner to provide that the fuzes rest on their booster end. This is done to keep the weight of the body of the fuze off the firing pin shear pin, which condition exists if the fuze is resting on its nose in the partially prearmed condition.

General. Fuze Mk 152 Mod 0 is completely armed when the striker flange has moved away from the edge of the outer sleeve a distance of 5/16 inches and the lower gear and carrier rotated about 345 degrees. If the striker flange has moved away from the outer sleeve more than 5/16 inches, the fuze should be regarded as armed. If it has not moved more than 3/16 inches, the fuze may be considered as partially armed. If the fuze is accidentally armed, whether assembled in the rocket head or not, no attempt should be made to unarm it except by Explosive Ordnance Disposal Personnel. In the event Ex-plosive Ordnance Disposal Personnel are not available the armed fuze (or rocket contain-ing an armed or partially armed fuze) should be disposed of by lowering gently into deep water, base downward.

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

1. Remove the dummy nose plug from the rocket head nose adapter and inspect the liner and threads and clean, if necessary. The cavity liner is to contain one Auxiliary Booster Mk 2, one Auxiliary Booster Mk 3, and a cardboard spacer approximately ½ inch thick placed below the auxiliary boosters. Tests have indicated that a high order detona-tion can still be expected if an additional cardboard spacer is used in place of the Auxili-ary Booster Mk 2; however, use of the booster is preferred.

2. Remove the fuze from the container and examine to see that the fuze is not dama-ged. If defective, repack, seal, and return to an ammunition depot.

3. Screw the fuze securely into the nose of the rocket head, using a spanner wrench to tighten.

4. After the round is placed on the launcer, remove the safety band.

5. Check the arming pin to ascertain that it passes through the striker flange and the vane carrier, and that it is secured by a Fahnestock clip resting snugly against the vane carrier.

6. Attach the ring of the arming pin (which extends toward the base of the fuze) to the arming  wire.

Removal from round. The fuze may be removed from the rocket head in the follow-ing manner:

1. Detach the arming wire from the ring on the arming pin.

2. Replace the safey band.

3. Remove the round from the launcher and remove the fuze with the proper spanner wrench.

4. Place the fuze in its shipping can and seal the can with adhesive tape along the broken surface.

5. Reassemble the dummy nose plug into the rocket head.

Packing. Each fuze is hermetically sealed in a metal can. Six cans are packed in a metal packing box, and four packing boxes are placed in a shipping box 25.8 inches by 17.6 inches by 15.1 inches which represents a total 4.0 cubic feet and a total weight of 177 pounds. The shipping cases containing Fuze Mk 152 are marked "For Use in 7.2-Inch Rockets Only".

Marking. Since the Fuze Mk 152 in stock were prepared by modifying loaded Bomb Fuzes AN-Mk 219, all markings indicating Fuze Mk 219 have been defaced and the letter-ing N.F. Mk 152 has been substituted.