Ordnance Pamphlet 909 is the Bureau of Ordnance technical manual for U.S. Navy 20-mm anti-aircraft gun mounts. It covers all marks in service — Mark 2 Mod. 2, Mark 4, Mark 5, Mark 6, and Mark 10 — with detailed chapters on description, construction, operation, lubrication, stripping, and reassembly for each. The manual includes full parts lists for all marks and a cross-index to OE and Bureau of Ordnance part numbers.
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