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PT Boat Armament
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PT boat .50 caliber turret gunner.
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Armament, 1942 ELCO 80' Patrol Torpedo (PT) Boat
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21 inch Mark 18-1 tube style launcher until PT 486, then lightweight torpedo roll-off racks (Mark 1?).
Higgins had 21" A.W. Mark 19 Mod 4 (22.5" diameter twin upper tubes, 1943)
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21 inch Mark 8-3C and D tube launched, then Mark 13 aircraft type with the roll-off racks.
Excerpt from MOTOR TORPEDO BOATS TACTICAL ORDERS AND DOCTRINE, July 1942:
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4110 (b) Torpedoes carried. Torpedoes carried on motor torpedo boats will consist of the following types:
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| Mark |
Diameter |
Length |
Speed |
Range |
| 8-3C and D |
21" |
256.3" |
27 knots
32 knots
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13,500 yards
9,000 yards (speed uses fuel up faster)
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| 14-1 |
21" |
246" |
28 knots
46 knots
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15,000 yards
4,500 yards
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| 15-1 |
21" |
288" |
35 knots
46 knots
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10,000 yards
6,500 yards
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A variant of the gun is the more common M2 HB (heavy barrel).
Aircraft type had:
- overall length 56.25" (HB 65.13") with a 9" shorter barrel (36" vs the HB's 45")
- full length drilled barrel jacket
- 23 pounds lighter (61 lbs vs the HB's 84 lbs)
- different style backplate/trigger assembly designed to fire simultaneously through mount linkages
- Faster rate of fire with slower speed
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Sketchy info on this, maybe Mark 17, Mod 1 (later type?) manual Scarff concentric ring mount.
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Mark 4, Mark 4/1 (parkerized coating, adaptor for modified lower double-loading stop plunger). Rate of fire 450rpm.
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Mark 4 height adjustable (about 16") trunnion mounted on the stern. Usually used without the 1/2" thick 250lb shield designed for it. This was a big heavy mount for this boat and it was replaced beginning with PT 372 by the Mark 10, a much lighter fixed height angle iron tripod style mount. A later version was the Mark 14, a lowered version of the M10 mount. The books Allied Coastal Forces volume II and Naval Weapons of WW2 have a lot of good images and information on this gun and mount.
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Mark 6 with a 300lb charge was the most common. Dimensions were 17.625" x 27.625" per Al Ross.
Excerpt from MOTOR TORPEDO BOATS TACTICAL ORDERS AND DOCTRINE, July 1942:
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4301. Types of depth charges. Depth charges carried aboard motor torpedo boats may be one of the following types:
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| Mark |
Weight of charge |
Depth Settings |
| 3 |
300 lbs |
50-300' |
| 6 |
300 lbs |
30-300' |
| 7 |
600 lbs |
30-300' |
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Ordinarily the 600-pound charges are not carried unless smaller charges are not available. The depth charge racks mounted on motor torpedo boats accommodate 300-pound charges only, and if 600-pound charges are carried, they must be lashed on deck.
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4302. Mark 6 charges.-Mark 6 charges should be carried whenever available, since the 30-foot depth setting is suited to shallow waters where motor torpedo boats are likely to operate.
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4303. Condition of readiness.-During peacetime, depth charges if carried on board, will have pistol and booster mechanisms removed and placed in designated stowage. During wartime depth charges will be kept either in the "normal" condition or the "ready" condition. (See Armament Conditions of Readiness.)
Large white marks extending from the depth setting graduations on the pistol and to the outer periphery of each charge should be painted with corresponding large white numbers denoting depth settings. This will facilitate setting depths at night.
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4304. Depth settings.-Normally the four forward charges should be kept set on 50 feet and the after four on 100 feet-depth of water permitting. This provides the best settings for the most likely encounter with enemy submarines, that of sighting his periscope close aboard or catching him on the surface at night. Under other conditions depth settings should be staggered among the charges on board. Charges should be dropped in rotation from each side working from forward aft. This will provide a pattern and tend to keep the boat on an even keel.
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Type C roll-off.
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Mark 3, will lay about 3 miles of smoke at top speed.
They were filled with titanium tetrachloride which combines with water or humidity to make large volumes of titanium dioxide (dense white) pigmented smoke. Also produced was hydrochloric acid so care had to be used in its handling.
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