Ordnance Pamphlet 820 is the official U.S. Navy description and operation manual for the 40mm Antiaircraft Gun — the Bofors-designed weapon that became the Navy’s standard medium-range antiaircraft gun of World War II. This complete document covers the Mark 1 and Mark 2 mechanisms in detail: the slide assembly, breech mechanism, loader, and recoil cylinder; the 40mm gun barrel Mark 1; the Mark 3 and Mark 4 sights; cyclic operation; loading and unloading procedures; casualty procedures; and full assembly and disassembly instructions for every major subassembly. The parts list and appendix (data sheet, lubrication, and variations) round out the manual.
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