If any of the shell fail to pass this test, the lot will be rejected.
The following extract from the "Circulars and Specifications of the Navy Department concerning Armor Plate and Appurtenances for Vessels of the U.S. Navy," (April 22, 1907) while pertaining to another subject, will be pardoned if introduced here for the purpose of demonstrating the seemingly paradoxical requirements a manufacturer is called upon to meet:
(Par. 60.) The ballistic test for acceptance of armor shall be made as strictly as practicable in accordance with the following tables, the Department reserving the right to use guns of other calibres than designated for any plate if it is deemed advisable.
In the test of armor of Class A there shall be three impacts with striking velocities as given in the following table, capped armor-piercing projectiles being used:
|
Wt. of shell capped Pounds |
Calibre of gun Inches |
Thickness of plates Inches |
Striking velocity Ft.-seconds |
| 105 | 6 | 5 | 1,451 |
| 105 | 6 | 6 | 1,648 |
| 105 | 6 | 7 | 1,836 |
| 165 | 7 | 6 | 1,464 |
| 165 | 7 | 7 | 1,631 |
| 165 | 7 | 8 | ,791 |
| 260 | 8 | 7 | 1,459 |
| 260 | 8 | 8 | 1,603 |
| 260 | 8 | 9 | 1,741 |
| 510 | 10 | 9 | 1,458 |
| 510 | 10 | 10 | 1,568 |
| 510 | 10 | 11 | 1,676 |
| 870 | 12 | 11 | 1,424 |
| 870 | 12 | 12 | 1,514 |
The first impact shall be located near the central portion of the plate, and the other two impacts shall be located as directed by the Bureau; no impact, however, to be nearer another impact or an edge of the plate than 3½ calibres of the projectile used.
On these three impacts no projectile or fragment thereof shall get entirely through the plate and backing, nor shall any through crack develop to an edge of the plate or to another impact.
From the above it is seen that a manufacturer supplying both armor-plate and shell to the Government is called upon to produce a shell with sufficient integrity to completely penetrate, and without breaking up, his armor-plate of sufficient thickness to resist that shell.
The capping of projectiles consists in placing over the point a cone or mass of metal of comparative softness. In the United States services soft steel is used for the purpose. Authorities disagree as to the exact function which the cap plays, some claiming it to act as a lubricating metal facilitating the passage of the projectile, others claim that it gives an initial shock to the armor-plate before the shell proper has struck it, which latter then strikes the plate in a state of molecular unrest, and, therefore, of impaired resisting power. Firing tests of shell at armor-plate at oblique angles have proven the capped shell superior, which would indicate that the cap in this instance at any rate is capable of securing a hold on the plate which the bare point of the shell cannot, in so much as uncapped shells glance off. At any rate capped projectiles are, on the whole, superior to the uncapped and the practice of capping is recommended as an additional advantage when used in conjunction with the improvements here-in-after described.