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| U.S. EXPLOSIVE ORDNANCE |
| PART 1 - PROJECTILES, PROPELLANT, AND PROECTILE FUZES |
| Chapter 3 - PROJECTILE FUZES |
| Section 3 - NOSE TIME FUZES FOR PROJECTILES |
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Mk 42 (Obsolete) |
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Projectiles used in |
12"/50 H.C. |
| 14"/45/50 H.C. | |
| 16"/45/50 H.C. | |
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Over-all length, inches |
3.54 |
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Diameter at base ogive, inch |
3.05 |
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Threaded length, inch |
0.81 |
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Threads |
7 R.H. |
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Weight, pounds |
2.5 |
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Material |
Brass |
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Setting times, seconds |
minimum, 0.6 |
| maximum, 45 |
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Description: The Nose Time Fuze Mk 42 was developed to supersede the Mk 18 when used in major-caliber H.C. projectiles, because of the erratic performance of the latter fuze when so employed. The fuze is generally similar to the Nose Time Fuze Mk 61, diffe-ring only in that the primary driving force of the Mk 42 is provided by a heavy mainspring instead of by centrifugal weights. The driving force for the clockwork mechanism thus becomes substantially independent of the rate of spin of the projectile, and is applied during the entire running time of the fuze. |
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In addition to the spring-driven feature, the Nose Time Fuze Mk 42 also differs from the Mk 61 in that a heavy additional hammer is located in the recess in the nose cap of the fuze. This hammer is attached to the nose cap by a spring. On set-back, this ham-mer stretches the spring and strikes the conventional hammer, giving it additional force in striking the setting lug. This feature was found necessary because the low set-back of major-caliber projectiles failed to proivde sufficient force for the usual hammer arrange-ment to disengage the setting lug from the setting pin. |
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Operation: The method of operation of this fuze is generally similar to that of the Nose Time Fuze Mk 61, except, of course, that the driving force is supplied by a main-spring. The force of set-back, when the gun is fired, causes the auxiliary hammer to des-cend against the main hammer, disengaging the setting lug from the setting pin. |
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Centrifugal force causes the center arbor detent to move outwards against its spring and out of engagement with the center arbor. The mainspring is then allowend to exert its force on the center arbor, actuating the escapement-controlled clockwork mecha-nism. All other features of operation are identical to those of the Nose Time Fuze Mk 61. |
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Remarks: This fuze is now considered obsolete. It was found during functioning trials that the auxiliary hammer did not function properly on set-back. The Nose Time Fuze Mk 62 is designed to supersede this fuze in major-caliber H.C. projectiles. |
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Figure 92. Nose Time Fuze Mk 42 |
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