January 12, 1943
Dr. James B. Conant
Office of Scientific Research and Development
1530 P Street
Dear Dr. Conant:
I am writing to lay before you a matter about which I have been thinking during
the past five months, and to ask for your advice.
When I began work on the Committee on Hyper-Velocity Guns last August, the idea
occurred to me that it should be possible to increase the velocity of a projectile
fired from a gun by use of the rocket principle. I made some calculations, which indicated
that an increase in velocity of 500 to 1000 feet per second might well be achieved
in this way. Since then I have learned that this suggestion has been made bother people,
no doubt by many. the ideas to which I have finally been led seem, however, to be
different from others on which work has been done, such as that of Sir Dennis Burney,
who has made use of a finned projectile in a gun, and of the Aberdeen Proving Ground,
which in 1935 and 1938 reported experiments on increasing the range of finned mortar
projectiles with use of rocket propellant. Mr. Piestrak, who has suggested a rocket
gun, may possibly have had a device in mind somewhat similar to mine.
My proposal involves a charge of rocket propellant in a chamber at the rear of
the projectile of a rifled gun, this chamber in the projectile being open to the gun
chamber, and the rocket propellant being ignited at the same time as the gun propellant.
The charge would weigh about 10 or 15% of the projectile weight, and would impart
an added speed of 500 to 1000 feet per second to the projectile. Thus for th eM-3
or N-1A2 37 MM gun, giving muzzle velocity 2800 feet per second with the 1.92 lb.
standard projectile and 3900 with the 0.95 lb. T24B3 projectile, a muzzle velocity
as high as 4900 feet per second might be obtained with a one-pound projectile with
the rocket propellant. I have examined rounds of ammunition for 37 MM cannon and have
made preliminary designs of rocket projectiles.. A suitable rocket projectile might
have the same size and shape as the M55A1 projectile, except that the taper at the
base would not be present and the rotating band would be moved forward by 1 1/4 inches
to a point 3 1/2 inches from the base. The rear 3 1/2 inches of the projectile would
comprise the rocket motor, carrying 0.15 lb. of propellant, and the front 2 1/2 inches
might consist of a tungsten carbide armor-piercing core and a windshield. The stability
of this projectile in flight should be satisfactory. The charge of 0.15 lb. of propellant
would give a velocity increment of 100 feet per second to the one-pound projectile.
There is needed a propellant which can withstand
the rotational and set-back forces (perhaps by being cemented to the chamber) and
the high gun-chamber pressure of about 40000 psi. Whether an existing propellant can
be used or a new propellant must be developed could be decided by a program of experimental
work which would fit in well with our present NDRC program, if authorization to work
on the development of this new weapon were given.
It is important to note that the proposed change in the ammunition is simple,
and that this method of obtaining hypervelocities would be applied to any cannon without
any change whatever except in the ammunition. It is this latter feature of the proposed
weapon, which it holds in common with the new light-weight armor-piercing projectile,
which would make it especially liable to adoption by the armed services for use in
I have considered the various difficulties which suggest themselves and have
reached the conclusion that there is a reasonable chance that they can be overcome.
Most of these difficulties relate to the propellant.
So far as I am aware, no work along these lines is being done by anyone, although
some work is being done on other rocket-gun combinations. I do not know which division
of the NDRC this proposal should be laid before. Would you please tell me to whom
I should present this proposal in detail. I shall be in Washington for a Division
8 meeting on January 22, and plan to stay until the 25; this would give me the opportunity
to discuss the proposal with the proper persons.
I believe that, with the experience which we have had, we could answer the question
as to whether the available rocket propellants could be used in this way in a short
time, and at small cost.