General Data

Rockets Used In. 5.0-in. Surface High Capacity Spin-Stabilized Rocket (5.0-in. Rocket Head Mk 10 and Mods; 5.0-in. Rocket Motor Mk 4 and Mods).

Markings

Mk 173 Mod _____

Model _____ Lot _____

Over-All Dimensions and Weight

Weight

2.52 lb.

Material. Green ethyl cellulose plastic nose ogive molded integral to steel base ring; nose cap molded into the inside forward end of plastic ogive; steel body cylinder.

Arming Range. The arming range is 1800 to 3000 yards, with 50% of operable rounds armed by 2500 and 90% armed by 3300 yards. These arming distances are based on standard conditions of 70° F. propellant temperatures. Tests indicate that the arming time will be sightly earlier when the rounds are at temperatures below 70° F.

Compression-Type Waterproofing

Mods 2 and 4 only

Description

The operation of the VT Fuze Mk 173 is very similar to VT projectile fuzes. The differen-ces are in the internal construction, particularly the amplifier circuit; and therefore other marks of VT fuzes are not interchangeable with the Mk 173. Neither are VT Fuzes Mk 173 interchangeable with other mechanical-type fuzes, because of the fuze cavity size. Ano-ther difference between the Mk 173 and other VT projectile fuzes is the means provided for breakage of the electrolyte ampoule in the energizer. In the Mk 173 the ampoule is broken by a spin breaker. See Chapter 2, page 3. The distribution of the electrolyte to the cell plates is caused by centrifugal force as in wet-energizer VT projectile fuzes.

Employment

The VT Fuze Mk 173 is for use in ground-to-ground or ship-to-shore bombardment against personnel, light armament, and equipment. VT Fuze Mk 173 are not satisfactory for use against aircraft, becuse of their long arming time. Such use is not reommended.

Range characteristics and ballistics for the 5.0-in. rocket (5.0-in Rocket Head Mk 10 and Mods; 5.0-in. Rocket Motor Mk 4 and Mods) using VT fuzes are similar to rounds with point detonating fuzes sich as the Mk 30. A summary of characteristics, with limitations at propellant temperatures of 70° F., is as follows:

It will be noted that at ranges less than 3300 yards, VT fuzed rounds become slightly less effective. This is due to after-burning of the propellant grain, which prevents com-plete arming of the VT fuze. This characteristics is less evident at propellant temperatu-res above 70° F., because faster burning takes place. This characteristics is more pron-ounced at lower temperatures. The height above ground at which this fuze will operate varies from 15 to 75 feet, while over water the burst heights will generally be a little hig-her. The average height of burst is about 40 feet from the ground or water surface. Fu-zes may function if the trajectories pass within 400 feet of hill tops, ridges, or tree tops. For high-angle approach to dense foliage, bursts will occur around tree-top level, with bursts occurring higher for lower approach angles.

In salve fire from Reel Feed Automatic Launchers Mk 51, the premature score may in-crease to 30%, with a four-foot lateral spacing between simultaneously firing launchers. With a lateral spacing of fifteen feet and a longitudinal spacing (along line of fire) of twelve and one-half feet fo ??illegible word?? Launcher Mk 51, the normal incidence of ??illegible word?? 15% prematures for rapid salvo fire has been obtained in tests. Nor sal-vo effect tests have been performed with the Launcher Mk 102.

Safety

The VT fuze Mk 173 is armed only by the spin (approximately 80 r.p.s required to arm) of the rocket after launching. This fuze contains the standard Auxiliary Detonating Fuze Mk 44 which is also armed by spn of the rocket.

When a rocket round misfires in the launcher the entire round shall be disposed of in ac-cordnance with instructions on OP 1260.

When a rocket round is not fired, the round shall be removed in accordance with instruc-tions in OP 1260. The VZ Fuze shall not be removed from the rocket for stowage. Unu-sed round shall be carefully restowed to afford maximum protection from heat, moisture, and salt spray.

Personnel shall take cover during rocket firing of fuzed rounds, because of possible pre-mature bursts of rounds at about 300 yards from the launcher. The fragment back spray from such a burst may be dangerous. Safety features should prevent bursts from occur-ing closer than 300 yards to the launcher.

Safety precautions regarding rocket motors, etc., are given in OP 1260.

Remarks

The Mk 173 Mod 0 does not have the wave-suppression feature or compression-type waterproofing. Mod 2, which is not expected to be issued, has compression-type water-proofing but does not have the wave-suppression feature. Mod 4 has both the wave-suppression feature and compression-type waterproofing. Because of the longer body cylinder necessary for compression type waterproofing, Mods 2 and 4 are not physically interchangeable with the Mod 0. All Mods employ essentially the same frequency. At the present time only the Mod 0 has been issued.

Figure 14. VT Fuze Mk 173.