A delayed blowback breech lock designed by John Bell Blish, Commander, USNR in 1915. This system incorporated a phosphor bronze “H” shaped piece that rode in slots within the actuator and bolt on Thompson sub-machine guns. The purpose of this piece was to absorb the force produced by the gases, and due to the difference in angles, the piece was forced upwards and only slightly back. The theory was that the greater the force, the more the “H” piece jammed. The dissimilar metals were supposed to adhere while under pressure. At lower pressures, it moved freely to allow rearward movement of the bolt [15].
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