Mk 157 Mods 0 and 1, and Mk 159

Rockets uses in

Functioning

Fuzed used with

Arming Time

Body diameter, inches

Over-all length, inches

5-1/2

General: The Base Fuze Mk 157 Mod 0 is essentially similar to the Base Fuze Mk 146, with the following differences: (1) a 0.02-second delay detonator replaces the non-delay detonator of the Mk 146; (2) the firing pin and the firing-pin body are pinned together by a thin lock wire. The Base Fuze Mk 157 Mod 0 has been developed to afford greater pe-netration of the target than was possible with the non-delay detonator of the Base Fuze Mk 146. The Base Fuze Mk 157 Mod 0 is being replaced by the Mk 165 Mod 0, which con-sists of the Mk 157 Mod 0 with a motor adapter and an improved detonator-shutter lock-ing arrangement.

The Base Fuze Mk 157 Mod 1 differs from the Mk 157 Mod 0 in that the material for the fuze body has been considerably strengthened, and the number of external threads has been approximately doubled. In all other respects the fuze are identical.

Mk 159: The Base Fuze Mk 159 is similar to the Mk 157, except that the delay time has been changed to 0.015 second. The fuze is used in the base of the 5.0-inch Rocket (5.0-inch Motor - Head Mks 5 and 6). Other minor structural changes have been made as follows: (1) a slightly heavier shear wire is used; (2) the inlet screen and inlet washer have been replaced by a brass washer having one side flat and the other radially serrat-ed (the radially serrated side faces the fuze head, so that the motor gases can enter the fuze diaphragm chamber); (3) the number of external threads on the body has been in-creased and "run out" just below the flange to afford a snug fit for the sealing washer, and (4) the fuze has been completely waterproofed. The Base Fuze Mk 159 is shipped to the field installed in the base of the rocket head.

Remarks: The sensitivity of the Base Fuze Mk 157 Mod 0 is somewhat less than that of the Base Fuze Mk 146, since the percussion-type primers used in delay explosive trains are inherently less sensitive than the "stab"-type primer caps used in instantane-ous detonators.

The Base Fuzes Mk 157 Mod 0 and Mk 157 Mod 1 are always shipped to the field in-stalled in the base of the rocket.

No attempt should ever be made to remove this fuze from the assembled round for any purpose prior to firing, e.g., to clean the fuze or substitute a base plug for the fuze. Anything less than a perfect seal between the fuze and the adapter in the base of the rocket body will allow the gases from the rocket motor to seep into the body and contact the H.E. filling. Premature explosion of the rocket is then highly probable.

Figure 163. Navy Base Fuzes (Rocket) Mk 157 Type