Practice Bomb Signals (Navy)

AN-Mk 4 and AN-Mk 5: For the miniature practice bombs, these signals allow obser-vers to spot the impact of salvos. The Practice Signal Cartridge AN-Mk 4 is an extra long 10-gauge shotgun shell which is inserted in the nose of the bomb. On impact, the cart-ridge is fired, expelling a large pull of black smoke from the tail of the bomb. The firing device consists of two shallow cups separated by a space, the firing pin extending through the bottom of one cup. The Signal Cartridge Mk 5 is the same size but filed with fluorescein, which stains the water, giving a spot of longer duration than the AN-Mk 4.

Mk 6 Mod 0 and Mk 7 Mod 0: These signals are essentially cans of black powder fit-ted with the Fuze Mk 247. The Mk 6 is used in the Practice Bombs Mk 65 and Mk 66; the Mk 7 in the Bomb Mk 15 Mod 3. They are attached to the rear of the bomb by brackets or a strap arrangement. The Signal Mk 7 is 13.08 inches long and 2 inches in diameter. It has a total weight of 2.5 pounds. It has a filling of one pound of black powder. The Mk 6 generally the same, except that the fuze is mounted off-center and the black-powder filling weighs two pounds.

The Fuze Mk 247 consists of an inertia weight held by a jump-out pin and a creep spring. The detonator is a blank caliber .38 cartridge. When the signal is placed in the bomb, the firing pin assembly is unscrewed and a blank caliber .38 cartridge inserted in the cartridge chamber. The firing assembly is then re-inserted and secured by means of a lock nut. At the time of loading the bomb into the plane, the arming wire is inserted through the jump-out pin, and the safety pin is then removed. Upon release from the plane, the arming wire is withdrawn, allowing the jump-out pin to be thrown free, arming the signal. Upon impact, the weighted firing pin overcomes the creep spring and impinges upon the primer of the caliber .38 blank cartridge, which, in turn, ignites the main black-powder charge.

Figure 312. Practice Bomb Signals Mk 6 Mod 0 (left) and Mk 7 Mod 0 (right)

Figure 313. Fuze Mk 247 for Practice Bomb Signals, Mk 6 Mod 0 and Mk 7 Mod 0