Ordnance Drawing No. 4391 is the U.S. Navy descriptive handbook for the 40-mm anti-aircraft quadruple (quad) gun mount Mark 2 — the four-barrel Bofors mounting that became the standard heavy automatic anti-aircraft battery aboard battleships, cruisers, carriers, and destroyers in World War II. The manual is organized in three chapters covering the construction of the mount, its operation, and its assembly: stand, base ring, training circle, carriage, training and elevating gear, buffer and centering device, platform, operator’s seats, cooling system, and firing mechanism, followed by manual, power, and director (electrical) firing.
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