The 3.5" rockets were originally designed to be used against smaller targets such as submarines and tanks. For larger targets such as transports and light warcraft, the 5.0" warcraft, the 5.0" was developed from the 5" Mk 35 anti-aircraft shell. The 3.5" Mk 8 solid head and the 3.5" Mk 6 FS smoke filled are the only ones now being issued. The 3.5" H.E. heads were replaced by the 5.0", the former never being issued because of the small load of TNT carried as compared to the 5.0" heads.

TABLE ON ROCKET HEADS AND MOTORS

Head

Head
Wt.

Filling
Wt.

Head
Length

Total
Weight

Total
Length

Fuzing

3.5" Mks 1, 2

3.5" Mks 3, 5

3.5" Mk 4

3.5" Mks 6, 9

3.5" Mk 8

5.0" Mk 1

Mk 165

All heads use the 3.25" Motor Mk 7
(Motor Length: 46 in; Motor Weight: 33.8 lb.)
* Length includes the Mk 148 fuze.

ROCKET HEADS:

3.5 Mks 1 and 2: The head is of solid steel and contains no high explosive of fuze. The shape of the round gives a relatively long under-water travel at shallow depth of entry angles (about 20 degress), and it is used as a semi-amor piercing projectile against submarines or tanks. The Mk 1 was the CIT production which was adopted by BuOrd and designed the Mk 2.

3.5" Mks 3 and 5: The head is filled with TNT and fitted with an adapter in the nose to take the Mk 149 fuze. With a second adapter, the diameter is reduced to 1.5 in. to take the Mk 148 fuze. These rounds were not issued and were replaced by the 5.0" heads which contains a greater load of high explosive.

3.5" Mk 4: The head has a semi-armor piercing nose and is fitted with TNT. This round was not issued of small load of high explosive and was replaced by the 5.0" heads.

3.5" Mks 6 and 9: The head is filled with FS smoke. The Mk 9 was the initial CIT pro-duction but was not issued. BuOrd in adopting this head, increased the length 1½" and issued the round as the Mk 6.

3.5" Mk 8: The head is of solid steel and contains no high explosive or fuze. The round was developed to give better underwater travel and will replace the 3.5" Mk 2.

5.0" Mk 1: The head is filled with TNT and weighs 46.5 lbs. when fitted with a Mk 148 fuze. The same adaptor rings are used as on the 3.5" Mk 5. Head issued with nose plug. Nose fuze must always be assembled in head before firing. Fire with fuze on "safe" if delay is desired. Head shipped with base fuze sealed in place. Base fuze must not be removed.

5.0" Mk 1 Mod 1: This head differs from the 5.0" Mk 1 Mod 0 only in that the nose is especially cavetized to take the Mk 172-0 fuze which is larger than the Mk 149 or other nose fuzes and therefore is not interchangeable with them.

3.25" Mk 7 Motor: (See drawing page 30)

The 3.25" Mk 7 motor is used with the 3.5" and 5.0" heads described above. At the forward end of the Motor is a black powder igniter and an electric squib. Two electric leads extend through the motor and out the aft end to a cable and plug connection. At the aft end of the motor there is a venturi tube which acts as a nozzle, and a bag of silica gel which acts as a dehydrating agent in keeping moisture from the ballistite grain. The ballistite grain used is the cruciform type with inhibitors, being 33" long, 2.75" in diameter, and weighing 8.5 lbs. Burning time of the ballistite varies from .62 seconds to 1.46 seconds, depending on the temperature.

The tail consists of 4 sheet metal fins set 90° apart and welded to a central cylin-der. The tail is slipped over the aft end of the motor and is secured by a tail locking ring, which screws on.

REMARKS:

(1) CIT refers to the California Institute of Technology which develops rockets for the Bureau of Ordnance. As the rockets are adopted by BuOrd, new mark or mod num-bers are assigned.

(2) Rockets fired from aircraft are more accurate than those fired from the ground. The 3.5" fired from an aircraft traveling at 300 to 500 ft/sec has a mean deviation in dispersion of about 5 mils; when fired from the ground, the dispersion is 26 mils.

(3) The 3.5" (H.E. and FS) have a maximum velocity of 1200 ft/sec. exclusive of plane speed as compared to 800 ft/sec. for the 5.0" H.E.