A New and Improved Cavity Charge Projectile

Notes on explosives, October 2, 1942.

Major Ross, patent attorney for the Navy…said that perhaps I didn’t know that I was co-inventor in this invention – I do not remember having been told that I was. The invention is on an offset liner for cavity charge.

-Linus Pauling, February 8, 1952.

In February 1952, Linus Pauling was summoned by K.F. Ross, patent attorney for the Navy, to sign an oath and patent application form. The document was titled “Oath, Power of Attorney, and Petition,” and stated that Pauling and Martin A. Paul were the joint inventors of “An Offset Liner for a Cavity Charge Projectile.” Paul had already signed the same application on January 17, 1952. The document also stated that D.C. Snyder and K.W. Wonnell, attorneys affiliated with the Office of Naval Research, would manage the patent application.

When the inventors signed the patent application form, they also agreed to sell their invention to the Navy, which bought the patent from them for the sum of one dollar. It was furthermore stated that

The said Owners hereby agree to execute and deliver unto the Government, upon request, any and all instruments necessary to convey to the Government the full right, title, and interest in and to any substitutions, divisions, or continuations in part of said application.

In this way, Pauling simultaneously claimed inventorship and signed away ownership, as well as any other claims to the invention, with one stroke of his pen.

As a war-time scientist, Pauling was often called upon by the U.S. government to aid in the defense and protection of the country. During World War II he worked on projects as diverse as an oxygen meter and a human blood substitute. The offset liner for a cavity charge projectile, which Pauling worked on with Martin Paul, was one such project. The timing of the application, coupled with the absence of the cavity charge projectile from Pauling’s research notebooks, suggest that this was another of Pauling’s war work projects, but one that remained top secret until after the war.

The problem that the researchers endeavored to solve was the stabilization of gun-ejected explosive shells. The contemporary method of stabilization upon which Pauling and Paul were charged to improve was to spin the shells as they were ejected, which was not very efficient. For one, spinning the shells resulted in a fifty percent decrease in the force that the shells could deliver upon impact, as compared to a shell that does not spin. Working together, Pauling and Paul found a creative way to provide stabilization without lessening the impact that the shells could make on their targets.

Diagrams included with Pauling and Paul’s cavity charge projectile patent, November 1965.

The primary object of their project was to improve the penetrating power of a spin-stabilized, cavity charge explosive shell by inventing an improved cavity-charge shell. A cavity-charge shell includes a space around which the explosive is arranged, so that when the explosive detonates, the shaped cavity focuses and increases the detonation, thereby requiring a smaller amount of explosive to deliver a comparable amount of force.

One tactic used by Pauling and Paul in pursuit of increased efficiency was to change the shape of the cavity’s liner. The new and improved model of a cavity-charge projectile utilized a plurality of offset plane sectors which faced in the direction of the shell’s rotation, ostensibly causing the shell to be slowed less by spinning.

Further, in Pauling and Paul’s model, the liner for a cavity-charge projectile was constructed by dividing the conical surface of the cavity into sectors, and tilting each sector slightly towards the preceding sector. According to the duo’s patent, “45 degree steel cones of .062 inch thickness and sectioned in half and in quarters were respectively put together again with silver solder in such a way that adjoining edges were offset with respect to each other.” Upon impact, the force exerted by the explosive in the shell on these sectors would compensate for the slowing of forward motion caused by spin.

Pauling and Paul had been constructing cavity liners by dividing a conical surface into four separate sections which were then twisted or canted relative to each other. But the patent states that a die could be constructed which would enable the structure to be made in a single stamping. As to the efficiency of the offset cavity liner, “It can be seen that for speeds of rotation above about 130 r.p.m., the modified cones were far superior to the unmodified cones.”

Diagrams included with Pauling and Paul’s cavity charge projectile patent, November 1965.

Several variations in the invention emerged with slightly different cavity shapes and other modifications, but the patent concludes that the various versions of the invention all had key features in common. For one, all of them required the offset surface to face the direction of rotation of the shell. Likewise, they required “that there be a plurality of offset sectors where the amount of offset increases from apex to the base of the shell head portion.”

Pauling and Paul’s joint invention, “An Offset Liner for a Cavity Charge Projectile,” U.S. patent number 3, 217, 650, was patented on November 16, 1965, thirteen years after the original application was filed.