20 MM Antiaircraft Gun Mount, OP 909, 1943, is a Navy service manual for the anti-aircraft gun of choice during the early years of WW II.
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Operation No. 24, second line-changeoiler (OE-2138)to readplug (299759-5).
45
Operation No. 29, first line-after word screws add(367557-8).
45
Operation No. 33, first line-change(OE-2158)to read(299948-1).
51
Operation No. 1, between lines (c) and (e)-add(d) Place spacing ring (OE-2067) on spring (OE-2062).
Plate 1 at p. 56
Left end of plate, Section A-A-change top(OE-2168)(leading to the spiral spring housing bushing, printed in blue) to read(OE-2166).
Center of plate, list of part numbers starting with 299948-1-change(OE-2093)to read(OE-2036); change(OE-2030)to read(OE-2093).
Right center of plate, below handwheel, list of parts starting with (OE-2108)-change(OE-2142)to read(OE-2123)and(OE-2123)to read(OE-2142).
RESTRICTED
NAVY DEPARTMENT, BUREAU OF ORDNANCE, WASHINGTON, D.C.
To all holders of Ordnance Pamphlet 909
Insert change; write on cover "Change I entered.'
Approved by The Chief of The Bureau of Ordnance
OP 909 CHANGE 1
7 July 1944
Page -- Page 1
ORDNANCE PAMPHLET 909
is changed as follows:
MOUNTS-ASSEMBLIES -20 MM.
Mounts Mk 2, Mk 2 Mod 1, Mk 2 Mod 21
Mk 4, Mk 4 Mod 1, Mk 4 Mod 2, Mk 4 Mod 3;
Mk 5, Mk 5 Mod I, Mk 5 Mod 3, Mk 5 Mod 4;
Mk 6; Mk 10 and Mk 10 Mod 1 - Description
1. Wherever extra light mineral oil NS 1042, 2075, or 2110, or medium mineral oil NS 1065, or
3065 is now specified light preservative oil 0rdnance Specification 1362 should be used.
2. Wherever oil mixture OE 3533 is- now specified, transformer oil NDS 14-0-12 or a mixture of
85% extra light oil NS 1042, 2110, or 2075, and 15% Diesel fuel oil NDS -7-0-2 should be used.
3. Where anti-seize compound NS 52-0-19 (INT) is specified, bearing grease Ordnance Specification 1350 should be used.
ORDNANCE PAMPHLET NO. 909
MOUNTS
ASSEMBLIES
20 MM MOUNTS MARK 2, MARK 2 MOD. 1, MARK 2
MOD. 2; MARK 4, MARK 4 MOD. 1 MARK 4 MOD. 2,
MARK 4 MOD. 3; MARK 5, MARK 5 MOD. 1, MARK 5
MOD. 3, MARK 5 MOD. 4; MARK 6; MARK 10 AND
MARK 10 MOD. 1
DESCRIPTION
MARCH 1943
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PREFACE
20 mm. A.A. Gun Mounts Mark 2, Mark 2 Mod. 1, Mark 2 Mod. 2; Mark 4, Mark 4 Mod. 1, Mark 4 Mod. 2, Mark 4 Mod. 3; Mark 5, Mark 5 Mod. 1, Mark 5 Mod. 3, Mark 5 Mod. 4; Mark 6; Mark 10 and Mark 10 Mod. 1.
This Ordnance Pamphlet, No. 909, describes the construction, operation, and maintenance of the various 20 mm. A.A. Gun Mounts now in service.
Additional Ordnance publications relating to the use of the 20 mm. A.A. Guns and Mounts are:
O.P. 911-
20 mm. Machine Gun Mechanisms Marks 2 and 4;
20 mm. Guns Marks 2, 3, 4, and 4 Mod. 1;
20 mm. Sights Marks 2, 4, 4 Mod. 1, and 5;
20 mm. Hand Grips and Shoulder Rests Marks 2, 4, and 5.
O.D. 4429-
Gun Sight Mark 14 Mod. 2-Installation and Operation.
Sk. No. 103308-
20 mm. Machine Gun and Mount Index.
The Mark 2 Mount is built to British standards and specifications in this country, but it has been issued by the U. S. Navy as well as the British Admiralty. In this mount the trunnion height is varied by means of a handwheel operating, through a train of gears, a screw inside the stand.
The Mark 4 Mount is identical in operation and almost identical in appearance to the Mark 2 Mount. The Mark 4 Mount has the cocking cable wound around the stand and secured to a hook at one end and a snap at the other. The Mark 2 Mount Cocking Cable is secured to a spring loaded reel which is housed within the stand. The Mark 4 Mount is built to U. S. standards and specifications and is issued by both the U. S. Navy and British Admiralty.
Mark 5 Mount is a Fixed Trunnion Height type. The use of Mounts Mark 5 is a temporary expedient and these mounts will be replaced on Naval Vessels by Mounts Marks 2, 4, 6, or 10, when available. A limited number of Mark 5 Mounts have been issued for installation in Merchant Vessels and these mounts are considered to be practical for this purpose.
Mark 5 Mod. 4 Mount is for use on submarines. It is of the Fixed Trunnion Height type with a shorter pedestal than used on the Mark 5 Mount. Also it has a number of holes drilled in the pedestal to permit sea water to drain out when the submarine is surfaced.
The Mark 6 Mount is an Adjustable Trunnion Height hydraulically operated type. The height of the trunnion is varied by a hydraulic system operated by foot pedals located in the pedestal.
Mark 10 Mount is a Fixed Trunnion Height type. The stand is a weldment of steel stampings, instead of a casting such as used on other types of 20 mm. A.A. Gun Mounts.
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TABLE OF CONTENTS
NOTE-
Plate 1 is the folded insert of Marks 2 and 4 Gun Mount at page 56. Plate 2 is the folded insert of Mark 5 Mod. 3 Gun Mount at page 72. Plate 3 is the folded insert of Mark 6 Gun Mount at page 120.