Description
This fuze was designed to initiate detonation when passing within the maximum influence radius of about sixty feet. The Mod 40 has reduced sensitivity against low flying aircraft because of the wave suppression feature (for values, see VT Fuze Mk 40). Burst heights above water for all Mods without the wave suppression feature will be high at most ranges, averaging 130 feet at 12,200 yards in the 5"/38 projectile, with burst heights varying widely between rounds. Burst heights over water will average lower at shorter ranges, but a wide dispersion in heights will occur. These fuzes are especially affected by water surface conditions; Burst heights of the Mod 40 above water (WSF) will vary between 10 and 50 feet. Random premature bursts of rounds assembled with this fuze will occur along the trajectory after the fuze is armed but before it approaches a target. With targets at long range, 20 per cent of the rounds may burst before approaching the target, and a somewhat smaller percentage of prematures will occur at shorter ranges. If a target at long range is approached within the sensitivity limits of the fuze, 65 per cent of the rounds should function at the most critical point to throw fragments against the target. The percentage of proper functions at shorter ranges is higher by the amount of decrease in premature functions. The remainder of the rounds will be duds. Because of aging of the dry energizer, only about 50 per cent of the rounds will function properly after eight months. The dry energizers are changed about every six months by Bureau of Ordnance personnel. Production has been suspended on this item.
This fuze was used for antiaircraft work from 600 yards minimum range to extreme range. The Mod 40, with WSF, has normal sensitivity above about 200 feet from the water, but has automatically reduced sensitivity below this level. Mods 0-20 and 80 are not ordinarily used against surface craft, because bursts at long range are too high for effective fragmentation damage, and those on low trajectory have a large dispersion in range. These Mods might be used with reduced effectiveness against low flying planes.
The Auxiliary Detonating Fuze Mk 54, replacing the Auxiliary Detonating Fuzes Mks 17 and 46, is used in conjunction with this fuze.
All models require the Mk 54 AD fuze. There is no SD feature.
Functioning
When the round is fired, acceleration in the gun causes the three setback switches to close. This action connects the battery to the electrical mechanism and initiates charging of the firing condenser throughout its high resistance delay circuit. Simultaneously, the setback pin in the centrifugal clock moves back against its spring, freeing and starting the clock escapement mechanism. In the armed position, the setback pin is locked by the locking spring.
Centrifugal force drives the clock through its permanent setting of 0.4 to 0.6 second, at which time the tripping lever moves over the spring loaded arming pin. The arming pin moves forward, withdrawing from the interrupter cavity. This allows the interrupter pin to be moved outward by centrifugal force, thereby clearing the flash channel between the electric primer and the auxiliary detonating fuze, hitting the short circuit plug, and breaking the short circuit wire away from the electric primer leads.
Meanwhile, the firing condenser has been accumulating an electric charge. When this charge is sufficient to allow firing of the electric primer, normally 0.6 to 0.8 second in the dry battery type fuze, the fuze is fully armed.
On approach to a target under the proper conditions, the reflected electromagnetic signal from the target causes the VT element to discharge the firing condenser through the electric primer. The blast from the primer operates the auxiliary detonating fuze, which in tum initiates detonation of the projectile.
Operation of the wet energized fuzes of this type is identical, except that the electrolyte vial in the reserve energizer is broken by acceleration of the round, and centrifugal force distributes the electrolyte throughout the energizer. Charging of the firing condenser is not begun when the setback switches close, but must wait until the electrolyte is uniformly distributed through the reserve energizer. This normally occurs 0.2 to 0.3 seconds after setback, thereby delaying complete arming of the unit until 0.8 to 1.1 seconds after setback.
Hazardous Components
No information about hazardous components.
See Also
Nothing else to see.
Source(s)
MIL-HDBK-146, Fuze Catalog (1982)
OP 1664, Volume 1 - US Explosive Ordnance (1947)
