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PT Boat Armament
PT Boat Browning .50 Cal Gunner


Armament, 1942 Elco 80' Patrol Torpedo (PT) Boat
21" A.W. (above water) Torpedo Tube Mark 18 Usually used with the 21" diameter Mark 8 torpedo. Larger diameter launch tubes for the 22 1/2" Mark 13 torpedo were developed but only installed on a few boats before the approx. 540 pound roll-off racks were made standard which were capable of firing either 21" or 22.5" diameter torpedoes.

Weight: 1450 pounds.

Length: Less breech door: 242 7/8", to aft face of breech door: 244 3/4".

Tube: 1/8" wall steel, 21.15" I.D., 21.4" O.D..

Official drawings:

Torpedo 21" diameter Bliss-Leavitt manufactured Mark 8 tube launched was standard on early boats, then the 22.5" diameter Mark 13 aircraft type with the roll-off racks. The Mk 13 was available in limited numbers when the United States entered the war in 1941.


4110 (b) Torpedoes carried. Torpedoes carried on motor torpedo boats will consist of the following types:

Mark Diameter Length Speed Range
8-3C and D 21" 256.3" 27 knots
32 knots
13,500 yards
9,000 yards (speed uses fuel up faster)
14-1 21" 246" 28 knots
46 knots
15,000 yards
4,500 yards
15-1 21" 288" 35 knots
46 knots
10,000 yards
6,500 yards

Selected data from A Brief History of U.S. Navy Torpedo Development (sometimes called OP 353W or TD5436), 15 September 1978:

Data for torpedoes Mark 8, 13, 14, and 15
Mark Developed Diameter Length Weight (pounds) Speed (knots) Range (yards) Warhead Exploder
8 1911 21" 256.3" 2600 36 16,000 Mk 8 Mod 4, 466 pounds of TNT Mk 3 Mod 2
13 1936 22.5" 161" (162?) 2216 33.5 63,000 Mk 13, 600 pounds TPX Mk 8
14 1931 21" 246" 3209 Low 31.1
High 46.3
Low 9,000
High 4500
Mk 16 Mod 6, 643 pounds HBX Mk 6 Mod 13
15 1938 21" 288" 3841 Low 26.5
Medium 33.5
High 45.00
Low 15,000
Medium 10,000
High 6000
Mk 7 Mod 3, 825 pounds HBX Mk 6 Mod 13

Browning M2 .50 Caliber Machine Gun, Aircraft Type 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)
  • Usually a different style backplate/trigger assembly designed to fire through linkages
  • Faster rate of fire with slower speed
Machine Gun Turret Twin Mount Mark 17 manually operated Scarff concentric ring mount consisting of the carriage, Mark 9, the cradle, Mark 9, and the Sight, Mark 11. In addition to the rotation of the entire mount assembly, the cradle yoke also allowed a small amount of rotation.

Maximum elevation : 85 degrees

Maximum depression : 15 degrees but usually limited by the turret depression rails

Rotation by ring: 360 degrees

Rotation by yoke: 10 to 15 degrees depending on gun elevation

Gun spacing: 6.5"

Weight without guns, ammunition or protective shield: 495 pounds


Oerlikon Mark 4 20mm (.7898") AA Gun There was very little difference between the British and U.S.N. Mark 2 guns, and the U.S.N. Mark 4. The later Mark 4/1 has a parkerized coating and adapter for modified lower double-loading stop plunger.

Rate of fire: 450 rounds per minute.

Magazine capacity: 60 rounds.

Range (max at 45 degrees elevation): Approximately 4,800 yards.

Weight: With barrel having cooling ribs: 141 pounds. With solid barrel: 150 pounds.

Barrel length: 4', 9 11/64"


Oerlikon 20mm AA Gun Mount Mark 4 height adjustable (about 16") trunnion mounted on the stern. Usually used without the 1/2" thick 250lb shield designed for the mount. 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. Besides the manual, the books Allied Coastal Forces volume II and Naval Weapons of WW2 have good images and information on this gun and mount.


Depth Charge Mark 6 with a 300lb charge. Weight 420 pounds. Dimensions were 17.625" diameter, 27.625" length.


4301. Types of depth charges. Depth charges carried aboard motor torpedo boats may be one of the following types:

Mark Weight of charge Depth Settings
3 300 lbs 50-300'
6 300 lbs 30-300'
7 600 lbs 30-300'

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.

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.

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.

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.


THE MARK 6 depth charge consists of a 300 pound charge of TNT which is fired by a hydrostatically operated pistol through the usual detonator booster train. The Mark 6 pistol has a depth setting range of 30 to 300 feet.

THE MARK 6 MOD. 1 depth charge is identical to the Mark 6 except that it is fitted with a Mark 6 Mod. 1 pistol which has a depth setting range of 30 to 600 feet.

The Mark 6 Mod. 1 pistol differs from the Mk. 6 pistol in that a spring-loaded depth-controlling valve for deep-firing is installed in place of the inlet valve assembly of the original design.

THE MARK 7 charge is exactly the same as Mark 6 in all principal parts EXCEPT that it has a larger case and contains 600 pounds of TNT instead 300 pounds.

THE MARK 7 MOD. 1 charge is the same as Mark 7 EXCEPT that it is fitted with the Mark 6 Mod. 1 pistol.

All of these charges measure 27.625 inches long. They DIFFER in weight and in diameter of case as follows:

(a) Mark 6 and Mark 6 Mod. 1 each weigh 420 pounds complete-and are 17.625 inches in diameter.

(b) Mark 7 and Mark 7 Mod. 1 each weigh 765 pounds complete-and are 24.875 inches in diameter.


Depth Charge Rack Type C roll-off.


Smoke Generator Various types, 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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