US3913486A

US3913486A - Automatic delay graze sensitive fuze

Info

Publication number: US3913486A
Application number: US403140A
Authority: US
Inventors: Stephan Kosonocky; Lloyd D Post
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1973-10-03
Filing date: 1973-10-03
Publication date: 1975-10-21
Anticipated expiration: 1992-10-21
Also published as: USB403140I5

Abstract

An auto-delay fuze for initiation of a detonator in a projectile has a self-contained inertially responsive system capable of releasing a spring loaded, ball-detented, firing pin when the projectile decelerates on impact. The fuze utilizes spin detents to hold an impact responsive slider and plunger members in contact with the firing pin detents. Upon impact a ball-plunger mass moves the slider member away from the firing pin detents and locks the slider upon an axially aligned holder thus placing the projectile in a ''''commit'''' position. Functioning of the fuze is delayed until such time as deceleration forces of impact, holding the plunger in its detenting position, are overcome by a biased spring acting in an opposite direction on the plunger, thus causing the plunger to move and release the firing pin from its detent.

Description

tlnited States Patent Kosonocky et a1. Oct. 21, 1975 AUTOMATIC DELAY GRAZE SENSITIVE 3,726,229 4/1973 Kosonocky et al. 102/73 FUZE - Primar Examiner-Samuel W. En le [75] Inventors: Stephan Kosonocky' Whi an y g Lloyd D. Post Dovr; g? OfyNJ Attorney, Agent, or FzrmNathan Edelberg; Gibson,

Robert P.; Max Yarmovsky [73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC. [57] ABSTRACT An auto-delay fuze for initiation of a detonator in a [22] Ffled: 1973 projectile has a self-contained inertially responsive [21] A l N 403,140 system capable of releasing a spring loaded, balldetented, firing pin when the projectile decelerates on [44] gubhshed under the Tnal Voluntary Protest impact. The fuze utilizes spin detents to hold an img on January 1975 as document pact responsive slider and plunger members in contact with the firing pin detents. Upon impact a ball-plunger mass moves the slider member away from the firing [52] US. Cl.2 102/75; 102/78; 102/79 pin detems and locks the Slider upon an axially aligned [51] hilt. Cl. F42C U08 holder thus p g the projectile in a i p i [58] held of Search lO2/75 80 tion. Functioning of the fuze is delayed until such time as deceleration forces of impact, holding the plunger [56] References C'ted in its detenting position, are overcome by a biased UNITED STATES PATENTS spring acting in an opposite direction on the plunger, 2,130,720 9/1938 Junehans 102/79 thus causing the plunger to move and release the firing 2,359,752 1'0/1944 Del Prato 102/80 pin from its detent. 2,381,900 8/1945 Graumann et al..... 102/75 2,873,677 2/1959 Taylor et al. 102/75 6 Clfllms, 9 Drawlng Figures Q 74 6 & i a 5 4 76 54 2 4 2 6 r- 60 5 r .55 8 6 a? 76 g 64 5 S /02 2 S 30 s I00 i.

US. Pawn 0a. 21, 1975 Sheet 1 of 5 3,913,486

U.S. Patent 0a. 21, 1975 shw 2 of5 3,913,486

atfint Oct. 21, 1975 Sheet 3 of 5 US Patent 00:. 21, 1975 Sheet 4 of GOVERNMENTAL INTEREST The invention deseribed herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION Various means have been used in the prior art to improve the maximum effectiveness of a projectile warhead while maintaining safety in handling. Particular problems with regard to premature malfunction have occurred in transportation of munitions, in-bore failures, and inadvertent initiations short of a target. Inbore failures in prior art devices were frequently caused by the failure of a safety lock or locks to properly function under severe acceleration forces experienced in a launch environment. Premature initiation above the intended target in projectiles having graze sensitive impact fuzes was frequently caused by inadvertent impact with foliage and/or rain drops, thus resulting in a decrease of projectile effectiveness.

In addition prior art munitions utilizing impact sensitive fuzes had problems with maximizing their warhead effectiveness against targets having varying penetrability characteristics. For example, prior art munition with a chemical or pyrotechnic delay train pre-set for use against concrete bunker positions or tanks would be ineffective against a target located in tunnels and vice versa. The present invention overcomes many of the aforementioned problems by its unique design.

SUMMARY OF THE INVENTION The present invention relates to an automatic, graze sensitive, impact delay fuze for a spin launched projectile that can be used with maximum effectiveness against varying density targets. The fuze is operatively positioned within the projectile so that the fuzes and projectiles longitudinal axes are axially aligned. The fuze has a spin detented plunger member which operatively holds an internally tapered member and centrifugal spin responsive detents thereon. Plunger back up balls acting in a plurality of plunger ball grooves provide the fuze with an inertial vector force whose direction and magnitude are sufficient to give the fuze sensitivity to low angles of impact. In the fuzes safe" position a spring-loaded, ball-detented, firing pin is slidably held in a cocked position by a slider-plunger assembly. The slider-plunger assembly and the ball detents are spin responsive and upon projectile launch release the slider-plunger assembly and the ball detents so that the fuze will be placed in an armed position. Upon impact with the target, the slider-plunger assembly is placed in a commit" position so that upon decrease of the deceleration pulse of impact the slider-plunger assembly will operatively permit the firing pin to forcibly impact a detonator. The fuze provides an automatic selection of delay time equal to the duration of the impact deceleration pulse due to the resistance of the target and the opposing force of a compressed creep spring which acts on the plunger to release the firin An object of the present invention is to provide an auto-delay fuze which is inertially responsive to release a spring-loaded firing pin to impact'a detonator upon impact.

Another object of the present invention is to provide an autodelay fuze which is dynamically balanced by symmetry of design.

Another object of the present invention is to provide an autodelay fuze which will function as a result of diminution of axial deceleration forces.

Another object of the present invention is to provide an auto-delay fuze which is sensitive to graze impacts.

Another object of the present invention is to provide an auto-delay fuze whose time delay is a function of target thickness.

Another object of the present invention is to provide an auto-delay fuze capable of operating in a superquick mode when initiated by the flash of an external detonator.

A further object of the present invention is to provide an auto-delay fuze with minimum threshold firing pin stored energy having a sliding detenting member which enhances the probability of functioning during the penetration of a variable but relatively low density target.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an axial cross-sectional view of the autodelay graze sensitive fuze, taken along line 1-1 of FIG. 2, showing the fuze in its safe unfired position.

FIG. 2 is a transverse cross-sectional view of the auto-delay graze sensitive fuze, taken along line 2--2 of FIG. 1, showing how the biased spin detents and detent spring slider restraining fingers hold the slider member within the plunger slider cavity when the fuze is in a safe position.

FIG. 3 is a transverse cross-sectional view of the auto-delay graze sensitive fuze, taken along line 33 of FIG. 1 showing the plunger rear end with graze sensitive ball masses operatively positioned therein.

FIG. 4 is a transverse cross-sectional view of the auto-delay graze sensitive fuze, taken along line 4-4 of FIG. 1 showing the configuration of a detent washer, firing pin spring retainer, firing pin holder and firing pin spring in relation to the housing.

FIG. 5 is a transverse cross-sectional view of the auto-delay graze sensitive fuze, taken along line 5-5 of FIG. 1 in its safe position showing a top view of a detent spring disc with slider restraining fingers holding the slider.

FIG. 6 is a transverse cross-sectional view of the auto-delay sensitive fuze in its safe position, taken along line 66 of FIG. 1, showing the details of holder detent ball bores, detent balls, slider, and plunger in relation to the housing.

FIG. 7 is a partial cross-sectional view of the autodelay graze sensitive fuze, taken along line 2-2 of FIG. 1, in its armed position showing the detents displaced toward the housing and away from the slider.

FIG. 8 is a partial cross-sectional view of the autodelay graze sensitive fuze in its commit position, showing the creep spring compressed by the inertial movement of the plunger toward the creep spring as a result of impact with the target, the slider forcibly thrust upon the tapered shoulder of the holder, and the spring loaded firing pin detented by the ball detents.

FIG. 9 is a partial cross-sectional view of the autodelay graze sensitive fuze in its fired position, after decay of the deceleration forces, showing how the creep spring has forced the plunger back towards its original position with the slider remaining against the holder.

Throughout the following description like reference numerals are used to denote like parts of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1-6, a fuze assembly has a cylindrical housing 12 having a partially closed forward end 14 and a rear end 16. The rear end 16 is staked to a disc-shaped cover 18 which has an axial holder bore 20 therein. The forward end 14 has an axial retainer bore 22 therein which fixedly holds a spring retainer 24. Spring retainer 24 has an axial spring retainer flash bore 26 therein which communicates and is axially aligned with a larger spring retainer holder bore 28. A hollow cylindrical firing pin holder member 30 has a rear open end 32 which is fixedly held in the cover holder bore 20, and a forward open end 34 which is fixedly held within the spring retainer bore 28. Adjacent the holder forward end 34 is a tapered holder section 36 which has a shoulder 38' which abuts the rear end 40 of retainer 24. The firing pin holder member 30 has three equally spaced transversely positioned ball detent bores 42 (FIG. 6) which communicate with a central bore 44 in member 30. A hollow shaped firing pin 46 is biasedly positioned in central bore 44 by a compressed coil spring 48 which has a first end 50 abutting against a retainer holder shoulder 52 on retainer 24 and its second end 53 abutting a firing pin open rear end 54. Adjacent the firing pin open rear end 54 is an annular slopingly sided ball detent groove 56. When the fuze is in a safe position, firing pin detent balls 58 are partially held within detent groove 56 and the ball bores 42 by a tapered inner wall surface 60 of a tubular slider member 62. The slider tapered inner wall surface 60 slidably fits over the outer surface 64 of holder member 30. The firing pin 46 has an axial flash bore 66 and a transverse flash bore 68 which permits the retainer flash bore 26 to communicate with the holder central bore 44. Operatively positioned intermediate the cover 18 and the spring retainer 24 is a cylindrically shaped plunger member 70 which slidably fits inside of housing 12. Plunger member 70 has an axial plunger-holder bore 72 therein which slidably fits over the firing pin holder outer surface 64. The plunger forward end 74 contains therein an axially positioned plunger slider bore 76 which communicates with the plunger-holder bore 72 on one end and with a larger axial plunger-detent counter bore 78 on its other end. Two integrally formed radially disposed plunger-detent pivots 80 (FIG. 2) protrude from the plunger member 70 toward the housing forward end 14. A pair of nonsymmetrical U-shaped detent levers 82 are rotatably held on the pivots 80 by a disc-shaped plunger-washer 84 and rivets 86. When the fuze 10 is in the safe position, detent levers 82 are biasedly held against the tapered holder section 36 and intermediate the spring retainer forward end 40 and the slider 62 by a pair of detent springs 88. Detent springs 88 are bent and integrally formed from a detent spring disc 90. Spring disc 90 has in addition a plurality of radially positioned inwardly protruding slider-restraining spring fingers 92 which hold the slider member 62 so as to prevent its forward premature movement when the projectile is being launched. Aspiral-helix creep spring 94 is biasedly positioned intermediate the housing forward end 14 and the plunger-washer 84. The rear end 96 of plunger 70 contains a plurality of equally spaced, radially inclined, partially cylindrically shaped ball-caming grooves 98 therein (FIG. 3). lnterposed intermediate each ball-caming grove 98 and the cover 18 is a backup ball mass 100 which can roll therein. The plunger member 70 has a plurality of peripherally positioned longitudinal air release grooves 102 therein to permit the air to easily escape from the housing forward end 14 to the housing rear end 16 when the plunger 70 on impact moves firstly forwardly in response to the inertial decelerating force and secondly rearwardly in response to the biased spring restoring force of the creep spring 94. A detonator 104 is axially positioned below the holder rear end 32 so that it can be initiated by the firing pin pointed end 105 of firing pin 46 when the fuze 10 is fired.

FIG. 7 shows the fuze 10 in its armed" position, just after the projectile has been fired from a launching weapon and prior to impact upon a target. In this position the spin forces have acted upon the U-shaped spin detents 82 causing them, because of their nonsymmetrical weight distribution about pivots 80, to rotate so that their weighted ends 83 move away from the longitudinal axis of the fuze 10 toward the housing 12, to positions outwardly of the spring retainer 24.

FIG. 8 shows the fuze 10 in its commit position just after the projectile has impacted upon the target. In this position plunger 70 has moved in a direction to compress the creep spring 94 so that it is flat and also has moved the slider member 62 so that its tapered inner wall surface 60 is forcibly held upon the externally tapered holder section 36. In the commit position, the walls of the plunger bore 72 continue to hold the firing pin detent balls 58 in their firing pin locking position.

FIG. 9 shows the fuze 10 in its fired" position just after the decelerating forces of impact acting on the plunger 70 and the ball mass have decreased to a level less than the force exerted by the creep spring 94 acting on the plunger 70 thereby causing the plunger 70 to move back toward the cover 18 and exposing the firing ball detents 58 to the now unobstructed open space of the plunger-slider bore 76.

In operation the fuze 10 is armed when the detent levers 82 open outwardly against the bias of the detent springs 88in response to spin induced centrifugal forces impressed upon the projectile. The fuze 10 is operatively positioned within the projectile so that its longitudinal axis is axially aligned with the projectiles longitudinal axis. The outward movement of the detent levers 82 removes the interference against the spring retainer 24 which prevented axial movement of the plunger 70 until this time. The detents 82 are mutually interlocked and will not open when the projectile and the fuze 10 therein are inadvertently subjected to a unidirectional force such as is caused by lateral impact when the projectile is accidently dropped or roughly handled. In order for the fuze 10 to be placed into its armed position it must experience a sufficiently high level of spin such as seen in a launching environment. When the armed fuze strikes a target surface, the combined mass of the back-up balls 100 and the plunger 70 is driven forward by the deceleration force against the restraining force of the creep spring 94. When the plunger member 70 and the slider member 62 move forward, the firing pin 46 will still be retained by the detent balls 58 because the wall of the plunger bore 72 restrains the detent balls 58 from moving radially outward. When the plunger 70 and slider 62 members are both driven toward the housing forward end 14 as a result of an impact with a target, the tapered inner wall surface 60 of slider 62 frictionally locks on the tapered holder section 36 of the firing pin holder 30. After the target impact deceleration of the fuze decreases, the creep spring 94 returns the plunger 70 to its original safe or unactuated position, while the slider member 62 remains in the aforementioned locked forward position. The return of the plunger 94 to its original location without the slider 62 allows the detent balls 58 to be cammed by ball detent groove 56 into the space previously occupied by the slider 62, and thereby releases the firing pin 46 so that its pointed front end 105 will forcibly strike the detonator 104 which is axially positioned operatively thereunder.

In order to prevent the premature release of the firing pin 46, during the in-bore or the muzzle blast region of projectile travel, the spring slider restraining fingers 92, which are integrally formed from the spring disc body 90, partially overlap the slider 62. These restraining fingers 92 prevent the separation of the slider 62 from the plunger member 70 when vibration or stress surges associated with the launching or muzzle blast conditions tend to prematurely move the slider 62 forwardly in respect to the plunger 70. The restraining force on the slider 62 exerted by the fingers 92 is negligible in comparison to the inertial force of impact on slider 62. After decay of the decelerating forces, the creep spring 94 pushes the plunger 70 toward its original safe position while the slider 62 remains locked on the firing pin holder tapered section 36.

The fuze 10 can also be used as a component part of a superquick functioning point detonating artillery pro jectile. Under auto-delay operation an interrupter means (not shown) is inserted in the retainer flash bore 26 blocking the passageway. When the point detonating superquick mode of functioning on target is selected, the interrupter means is removed from the retainer flash bore 26. The flash generated by a point detonating element (not shown) enters the housing 12 through the flash bore 26, passes through the holder central bore 44 and through the firing pin axial flash bore 66, through the firing pin transverse bore 68, through the rear end of the holder central bore 44 directly into the detonator 104. The measurable time delay under the superquick functioning condition is generally less than 125 microseconds. Under the autodelay functioning condition a delay of 5 to 7 milliseconds is prevalent on relatively thin targets and longer delays of approximately 10 to milliseconds for heavy targets depending upon their resistance to penetration.

The foregoing disclosure and drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled in the art.

Having thus fully described this invention, what is claimed as new and desired to be secured by Letters Patent of the United States is;

1. An automatic, graze sensitive, impact delay fuze for actuating a spin launched projectile which comprises:

a housing for holding said fuze therein, said housing having a forward end and a rear end;

a cylindrically shaped plunger member slidably positioned in said housing, said plunger having a plunger forward end, a plunger rear end and a centrally positioned axially aligned plunger-holder bore therein, said plunger forward end having a plunger-slider bore larger than and axially aligned with said plunger-holder bore and communicating therewith, and a plunger-detent counterbore larger than, and axially aligned and communicating with said plunger-slider bore;

firing pin detent means axially positioned in said fuze for placing said fuze in a commit position after said projectile is launched and has impacted;

a detonator axially positioned proximate to the rear end of said plunger; and

biased firing pin means, operatively held by said firing pin detent means, for forcibly striking and exploding said detonator upon decrease of the decelerating forces of impact; and

spin detent means rotatably supported on said plunger member within said plunger-detent counterbore for holding said fuze in a safe position until such time as said projectile has seen a proper launch environment which includes;

a pair of nonsmmetrically U-shaped detent levers oppositely disposed and pivotally supported on said plunger member;

a disc shaped plunger-washer for operatively holding said detents to said plunger; and

a spring disc operatively positioned intermediate said U-shaped detents and said plunger-detent counterbore having a pair of detent springs integrally formed from said spring disc, said pair of detent springs biasedly holding said U-shaped detents so that said fuze is maintained in said safe position prior to said projectile being launched, and a plurality of radially positioned inwardly protruding restraining spring fingers operatively positioned intermediate said U-shaped detents and said plunger member for restraining said firing pin detent means so that said biased firing pin means will not be released by said firing pin detent means until said projectile impacts.

2. An automatic, graze sensitive, impact delay fuze as recited in claim 1 wherein the firing pin detent means comprises:

a cup shaped spring retainer axially and fixedly positioned in said housing forward end, said retainer having an axial flash bore therein which communicates with a larger axially aligned retainer holder bore;

a conically helically shaped creep spring biasedly interposed intermediate the forward end of said housing and said plunger-washer;

a tubular firing pin holder having a holder forward end fixedly held in said retainer holder bore and a holder rear end fixedly held in the rear end of said housing so that said holder is axially aligned in said housing and said plunger-holder bore, said holder having an externally tapered holder section proximate said holder forward end, and a plurality of equally spaced transversely positioned ball detent bores therein;

a tubular slider operatively positioned in said plunger-slider bore, said slider having a tapered inner wall surface which slidably fits over said holder and covering said plurality of ball detent bores when said fuze is in a safe position; and

a plurality of firing pin detent balls operatively positioned in said ball detent bores;

wherein said slider is forcibly moved toward said externally tapered holder section when said projectile impacts and locks thereon so that upon decrease of the decelerating force of impact said biased firing pin means can be forcibly moved toward and strike said detonator.

3. An automatic, graze sensitive, impact fuze comprising:

a hollow cylindrical housing including outer, front and rear walls, and containing a fixed axial tubular firing pin holder portion with at least one radial opening therein;

a rearwardly-biased firing pin slidably disposed in said tubular portion;

a detonator disposed adjacent to the rear end of said tubular portion, in line with said firing pin;

an annular plunger member slidably disposed in said housing between said outer wall and said tubular portion and having a plunger-slider bore in its inner wall opposite said radial opening when said plunger member is in a rearward safe position adjacent to said rear wall in the safe condition of the fuze;

a creep spring interposed between said plunger member and said front wall for biasing said plunger member rearwardly;

spin-releasable detent means locking said plunger member in said rearward safe position, said plunger member being adapted to move forward by its own inertia, after being released by said detent means at launch, at impact of said fuze with a target;

a detent ball disposed partially in said opening for locking said firing pin in a safe position spaced from said detonator;

first means carried by said plunger member for holding said detent ball in locking position in said safe condition of said fuze; said first means including a tubular slider positioned in said bore;

second means carried by said plunger member, spaced rearwardly from said bore, for holding said detent ball in locking position after the forward movement of said plunger member and said slider on impact; and

means for holding said slider in its forward position when said plunger member is moved rearwardly by said creep spring after impact.

4. A fuze as in claim 3, wherein said second means is a portion of the inner surface of said annular plunger member.

5. A fuze as in claim 3, wherein said last-named means comprises cooperating axially tapered surfaces on the outside of said tubular portion and the inside of said slider.

6. A fuze as in claim 3, wherein said plunger member having said plunger-detent counterbore at the forward end thereof; and

said spin detent means comprises an external rearwardly facing shoulder spaced from the forward end of said tubular portion, a plurality of spin detents disposed within said detent counterbore, and spring means biasing said detents inwardly behind said shoulder in the safe condition of said fuze.

Claims

1. An automatic, graze sensitive, impact delay fuze for actuating a spin launched projectile which comprises: a housing for holding said fuze therein, said housing having a forward end and a rear end; a cylindrically shaped plunger member slidably positioned in said housing, said plunger having a plunger forward end, a plunger rear end and a centrally positioned axially aligned plunger-holder bore therein, said plunger forward end having a plunger-slider bore larger than and axially aligned with said plunger-holder bore and communicating therewith, and a plungerdetent counterbore larger than, and axially aligned and communicating with said plunger-slider bore; firing pin detent means axially positioned in said fuze for placing said fuze in a ''''commit'''' position after said projectile is launched and has impacted; a detonator axially positioned proximate to the rear end of said plunger; and biased firing pin means, operatively held by said firing pin detent means, for forcibly striking and exploding said detonator upon decrease of the decelerating forces of impact; and spin detent means rotatably supported on said plunger member within said plunger-detent counterbore for holding said fuze in a ''''safe'''' position until such time as said projectile has seen a proper launch environment which includes; a pair of nonsmmetrically U-shaped detent levers oppositely disposed and pivotally supported on said plunger member; a disc shaped plunger-washer for operatively holding said detents to said plunger; and a spring disc operatively positioned intermediate said U-shaped detents and said plunger-detent counterbore having a pair of detent springs integrally formed from said spring disc, said pair of detent springs biasedly holding said U-shaped detents so that said fuze is maintained in said ''''safe'''' position prior to said projectile being launched, and a plurality of radially positioned inwardly protruding restraining spring fingers operatively positioned intermediate said U-shaped detents and said plunger member for restraining said firing pin detent means so that said biased firing pin means will not be released by said firing pin detent means until said projectile impacts.

2. An automatic, graze sensitive, impact delay fuze as recited in claim 1 wherein the firing pin detent means comprises: a cup shaped spring retainer axially and fixedly positioned in said housing forward end, said retainer having an axial flash bore therein which communicates with a larger axially aligned retained holder bore; a conically helically shaped creep spring biasedly interposed intermediate the forward end of said housing and said plunger-washer; a tubular firing pin holder having a holder forward end fixedly held in said retainer holder bore and a holder rear end fixedly held in the rear end of said housing so that said holder is axially aligned in said housing and said plunger-holder bore, said holder having an externally tapered holder section proximate said holder forward end, and a plurality of equally spaced transversely positioned ball detent bores therein; a tubular slider operatively positioned in said plunger-slider bore, said slider having a tapered inner wall surface which slidably fits over said holder and covering said plurality of ball detent bores when said fuze is in a ''''safe'''' position; and a plurality of firing pin detent balls operatively positioned in said ball detent bores; wherein said slider is forcibly moved toward said externally tapered holder section when said projectile impacts and locks thereon so that upon decrease of the decelerating force of impact said biased firing pin means can be forcibly moved toward and strike said detonator.

3. An automatic, graze sensitive, impact fuze comprising: a hollow cylindrical housing including outer, front and rear walls, and containing a fixed axial tubular firing pin holder portion with at least one radial opening therein; a rearwardly-biased firing pin slidably disposed in said tubular portion; a detonator disposed adjacent to the rear end of said tubular portion, in line with said firing pin; an annular plunger member slidably disposed in said housing between said outer wall and said tubular portion and having a plunger-slider bore in its inner wall opposite said radial opening when said plunger member is in a rearward safe position adjacent to said rear wall in the safe condition of the fuze; a creep spring interposed between said plunger member and said front wall for biasing said plunger member rearwardly; spin-releasable detent means locking said plunger member in said rearward safe position, said plunger member being adapted to move forward by its own inertia, after being released by said detent means at launch, at impact of said fuze with a target; a detent ball disposed partially in said opening for locking said firing pin in a safe position spaced from said detonator; first means carried by said plunger member for holding said detent ball in locking position in said safe condition of said fuze; said first means including a tubular slider positioned in said bore; second means carried by said plunger Member, spaced rearwardly from said bore, for holding said detent ball in locking position after the forward movement of said plunger member and said slider on impact; and means for holding said slider in its forward position when said plunger member is moved rearwardly by said creep spring after impact.

6. A fuze as in claim 3, wherein said plunger member having said plunger-detent counterbore at the forward end thereof; and said spin detent means comprises an external rearwardly facing shoulder spaced from the forward end of said tubular portion, a plurality of spin detents disposed within said detent counterbore, and spring means biasing said detents inwardly behind said shoulder in the safe condition of said fuze.