The 2.25 sub-caliber rocket for aircraft use was developed for training purposes. Ini-tially two types were designed to approximate the trajectory of both the 3.5" and 5.0" rockets; however, it is believed thus only one rocket will be standardized for future use. The rocket with Motor Mk 11 and the body Mk 3 Mod 2 is the assembly which pro-bably will be used in future training.

The Mk 1, a CIT production, was issued until adopted and issued by BuOrd as the Mk 3 Mod 2. The Mk 2, a CIT production, was designed as a slow sub-caliber rocket. The complete assembly for the latter is no longer available.

Motor

Body

Velocity

Approximates
Trajectory of:

2.25" Mk 10 or 11

2.25" Mk 1 or 3 (1.6 lbs.)

1150 ft/sec

3.5" Rocket (3.25" Motor)

2.25" Mk 12 or 13

2.25" Mk 1 or 3 (1.6 lbs.)

810 ft/sec

5.0" Rocket (3.25" Motor)

2.25" Mk 10 or 11

2.25" Mk 2 (8.6 lbs.)

810 ft/sec

5.0" Rocket (3.25" Motor)

The 2.25" Motor Mark 10 and 11 are similar to each other as are the 2.25" Motor Mark 12 and 13. The Motors Mark 10 and 11 differ from the Mark 12 and 13 in that the diameter of the nozzle on the letter are smaller and the weight of propellant of the Mark 10 and 11 is 1.75 lbs. as compared to the weight of 1.12 lbs. in the Mark 12 and 13.

The external dimensions of these rockets are the same. For recognition purposes, the 2.25" Motors Mark 10 and 11 are painted white with black fins while the Motors Mark 12 and 13 are grey with black fins.

MOTOR Mk 11 and Body Mk 2 Mod 3

Overall length of the rocket is 29 inches. Two button type lugs are provided on the motor tube spaced approximately 19 inches apart. Four fins are welded to the aft end of the motor tube and are not removable as is the case with most service rockets.

The 2.25" motor Mark 11 contains essentialy the following parts:

(1) Propellant. The propellant is an extruded cylindrical grain of ballistite weighing approximately 1-3/4 pound. Inhibitor discs cemented to the end of the grain contorl the burning areas.

(2) Igniter. A 14 gram black powder igniter in a plastic case is located at the forward end of the motor. This igniter is set off by an electrical squib.

(3) Grid. The grid supports the propellant grain. During burning it prevents the grain from sliding rearward and clogging the nozzle opening.

(4) Nozzle. The nozzle is a steel venturi through which the gases flow. It directs the gas jet in the desired direction and also provides for the expension of the gases in the exit cone.

(5) Nozzle Closure. The nozzle closure seals the rear end of the motor. It is crimped to the electrical pigtail, providing a moisture proof seal.

(6) Pigtail. The electrical extends from the nozzle end and is the same design as that used in service rockets.

When the body is screwed to the motor is assembly, a luting compound (white or red lead) is used to effect a tight seal between the two parts.

LAUNCHERS

Rocket launcher Mark 6 is actually an adapter for accommodatuing the relatively short 2.25" sub-caliber rocket to the Mark 5 Mod 1 zero length launcher. The rocket launcher Mark 6 is placed on the Mark 5 Mod 1 zero length launcher in the same manner as a standard service round would be installed.

The 2.25" sub-caliber rocket is inserted in the rail slot of the Mark 6 launcher and is secured by a shear wire (#13 gauge soft copper) which is inserted through a latch ar-rangement.

Another type adapter known as the Mark 6 Mod 1 consists essentially of a rocket launcher Mark 6 with a special attachment for use on the Grumann type zero length launcher.

The sub-caliber 2.25" Rocket will fit the rail type, 70 inch Rocket Launcher Mark 4 directly without the use of an adapter.