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 3605

General arrangement drawing: 440263

Sketch list of drawings & specs: 165109

Explosive components:

A sensitive stab type compound detonator Mk 23 Mod 0 (lead azide primer mixture, lead azide and tetryl)

Booster lead-in charge (tetryl)

Booster charge (tetryl 54 grams, approximately)

General. Fuze Mk 141 Mod 0 was developed by a modification of the Bomb Fuze Mk AN-M110A1 as a replacement for Fuze Mk 152. The fuze is water discriminating and so designed that it will not fire on impact with water but will be actuated by impact with the earth or soft sand, provided the water travel before impact is not more than twenty feet. Fuze action is instantaneous. Arming is accomplished solely by air travel.

Use. Fuze Mk 141 is used in the 7.2-inch High Capacity Fin Stabilized Surface Rocket Mk 1 Mod 1 (See OP 1415). The complete round is employed primarily for the destruction of underwater beach obstacles.

Functioning mechanism. The fuze is essentially contained in three main assemblies: the body which houses the arming mechanism, the adapter magazine in which the deto-nator shutter and lead-in disc are housed, and the magazine to which is assembled a threaded adapter for securing the fuze to the rocket head. These three assemblies are threaded in order that they may be assemblied together.

A propeller is secured to the arming hub which protrudes through the forward end of the fuze body. To the after end of the arming hub a stationary gear is fixed, so called because it does not move fore or aft. Threaded inside the arming hub is the arming sleeve to which the movable gear is fixed. The firing pins and firing wheel are secured to the arming sleeve by a copper shear wire and the firing pin extends through the firing pin guide into the detonator shutter cavity. Both the stationary gear and movable gear mesh with a pinion which rotates on a pin fixed to the body.

Extending rearward and secured to the firing pin guide are two projecting pins called a shutter hinge pin and a shutter stop pin. Under influence of a shutter spring the shutter, containing the detonator, is pivoted on the shutter hinge pin into the arming position and is stopped by the shutter stop pin after the firing pin is retracted. The lead-in-disc as-sembly which is below the shutter is held in place by the magazone and a shoulder in the magazine adapter.

Attached to the body is an arming wire guide. Until such time as the fuze is used a safety wire, passed through a hole in the propeller and through this guide, prevents the propeller from turning. On the launcher an arming wire is used in place of the safety wire.

Figure 21 – Nose Fuze Mk 141, External View

Arming. Arming is accomplished in two steps. First, the arming wire is withdrawn as the rocket leaves the launcher, and, in the second step, air travel rotates the propeller to retract the firing pin permitting the alignment of the detonator with the firing pin and booster lead-in.

The propeller, nut, outer ball race, arming hub, and stationary gear rotate as a unit, but cannot move forward or aft because of the collar on the arming hub. The movable and stationary gears mesh with the pinion gear, and, since the movable gear has one more tooth than the stationary gear (33 teeth for the stationary gear and 34 teeth for the movable gear), for each rotation of the propeller, the movable gear lags on tooth thus screwing the arming sleeve into the arming hub. As the arming sleeve moves for-ward, it moves the firing wheel forward and withdraws the firing pin from the shutter ca-vity. When the firing pin is withdrawn from the shutter cavity, the shutter is releases, and the shutter spring rotates the shutter into position against a stop pin. A shutter de-tent then engages a hole in the firing pin guide thus locking the shutter in this position. The detonator is now aligned with the firing pin and booster lead-in, and the fuze is fully armed.

The arming distance of Fuze Mk 141 as used in the 7.2-inch Rocket Head Mk 5 is over 300 feet.

Firing. Upon the force of impact the firing wheel is driven rearward which shears the copper shear wire and drives the firing pin rearward to pierce and fire the detonator.

Acceptance test data. Completely live loaded fuzes chosen at random from each production lot are installed in live-loaded 7.2-inch demolition rockets and the rockets fired into shallow water or shore. The angle of elevation of the rocket launcher should be approximately 25 degrees. Acceptance is based on a cumulative test plan designed to accept (95% of the time) lots in which 94% of the fuzes function satisfactorily. Lots poorer than 94% will be subject to rejection with lots 60% effective being rejected 90% of the time.

Sensitivity limits. The fuze is water discriminating and so designed that it will not fire on impact with water, but will be fired by impact with earth or soft sand, provided the water travel before impact is not more than twenty feet.

Detonator safety. Fuze Mk 141 is detonator safe. In the unarmed position, the deto-nator is out of alignment with the explosive train. The detonator is vented through a hole in the firing pin guide, thus should the detonator function prematurely, the force of the detonator will be dissipated away from the explosive components. The firing train cannot be aligned until the safety wire or arming wire, as the case may be, has been withdrawn and the propeller rotated 90 to 130 revolutions.

During shipping and stowage. Sample fuzes from production are subjected to rough handling tests which are considered to be more severe than conditions encountered in normal stowage and shipping. Failure to pass these tests shall be cause for rejection of the lot. The propeller is kept from rotating by a safety wire which is replaced by the arm-ing wire in preparation for firing.

General. If the fuze is accidentally armed, whether assembled in the rocket head or not, no attempt should be made to unarm it. If a gap of 1/8-inch or more exists between the striker and the arming hub, the fuze should be considered armed. If the fuze is arm-ed, turning the propeller counterclockwise as viewed from the forward end will cause the firing pin to pierce the detonator and explode the booster. Armed fuzes must not be fired from rocket launchers. If the fuze in an assembled round is armed accidentally, the firing wheel must be positively prevented from moving rearward, during handling by means of placing a spacer between the firing wheel and arming hub, such as to assure the preser-vation of the gap. Then carefully unscrew the fuze from the rocket taking care not to drop the round or the fuze on its nose or strike the fuze in any way.

Dud rounds should be treated with extreme caution. If the firing wheel is flush with the arming hub, the fuze is in a fired condition. In such a condition, the firing wheel should not be disturbed as the firing pin may be imbedded in the detonator and any mo-vement might create sufficient friction to initiate the detonator. The fuze or round should be disposed of by gently lowering base or tail down into deep water or by Explosive Ord-nance Disposal Personnel in accordnace with existing instructions.

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 and spacer from the rocket head and inspect the liner to see that the two auxiliary boosters, or the one booster with cardboard spacer, (the spacer being placed so that the auxiliary booster is against the fuze) are in place.

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 fit the holes in the adapter.

4. After placing the round on the launcher, insert the arming wire (which has been se-cured to the launcher) in the hole provided next to the safety wire. Remove the safety wire.

5. Place the Fahnestock clip on the arming wire and adjust the Fahnestock clip so the arming wire is slack and not just tight.

6. Cut off excess arming wire leaving two or three inches projecting out in front of the fuze. Remove any burrs on the end of the arming wire.

Removal from round. The fuze may be removed from the rocket head with the pro-per fuze wrench and returned to the shipping can. The closed shipping can should in turn be selad with adhesive tape along the broken surface. Before removal of the fuze from the round the safety wire should be replaced. The dummy nose plug must be replaced in the rocket head after the fuze is removed.

Packing. Fuze are individually packed in hermetically sealed cans. Twenty-four fuzes are packed into a box 25.5 inches by 16.5 inches by 9.7 inches which represents a total of 2.4 cubic feet and a total weight of approximately 107 pounds.

Marking. The fuze is marked or stamped with the letters NF, the mark, mod, and lot number, the manufacturers's initials or symbol, the initials or symbol of the loading facili-ty, the month and year of loading, the anchor stamp, and the inspector's initials.