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U.S.S. ARGONNE,    Flagship


to ComMTBron ONE
Conf. ser. (018) of
Pearl Harbor, T. H.
4 December 1941

From: The Commander Base Force.
To: The Director, Naval Research Laboratory,
    Bellevue, D. C.
Via: The Commander-in-Chief, U. S. Pacific Fleet.
Subject:     Motor Torpedo Boats - Disguising of Wakes of.

        1.  Success in reducing wake visibility would unquestionably reduce the probability of sighting a motor torpedo boat, and it is recommended that investigation of the subject be pressed.

Chief of Staff

Copy to:














Submarine Base
Pearl Harbor, T. H.
25 November 1941


From: The Commander Motor Torpedo Boat Squadron ONE.
To: The Director Naval Research Laboratory, Bellevue,D/C.
Via: (1) Commander Base Force.
(2) Commander-in-Chief, U. S. Pacific Fleet.
(3) The Chief of Naval Operations.
Subject: Motor Torpedo Boats - Disguising of wakes of.
Inclosure:    (A) Extracts from miscellaneous reports on Motor Torpedo Boat Operations and Exercises.

        1.  Since the arrival of Motor Torpedo Boat Squadron One in the Hawaiian Area, day and night operations have been engaged in with certain major subdivisions of the Fleet, Inshore Patrol Destroyers and the 58th Army Aircraft Bombardment Squadron. In every case it has been found that the greatest deterrents to effective Motor Torpedo Boat operations have been the noise of engine exhausts and the wakes. Even in daylight operations with the Army Aircraft Bombardment Squadrons, reports indicate that from altitudes of about 3000 feet the boats themselves are invisible but can be readily located by the wakes. Extracts from reports submitted on local operations together with extracts from intelligence bulletins are submitted, in inclosure (A), to substantiate the above.

        2.  This command has recently ordered, from the Navy Yard, New York, underwater exhaust systems which were developed and reported highly successful by Motor Torpedo Boat squadron TWO. It is understood that the installation of these systems will silence Motor Torpedo Boats up to speeds of about 30 knots. There still remains the wake problem to contend with and it occurred to this command that it might be feasible to color the wakes for short distances. If this were possible it is believed that the Motor Torpedo Boat would be a very valuable and highly successful weapon of attack at night, against surface ships. The experience of this squadron, during night operations against the Fleet, has been that in nearly every case if wakes could have been obliterated for even 1000 yards, attacks could have been pushed home to ranges where effectiveness was almost certain.




Subject: Motor Torpedo Boats - Disguising of wakes of.
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        3.  During investigation of means to color wakes undertaken by this command, it was learned that the Naval Research Laboratory has conducted experiments in coloring wakes and in reducing spume. It is therefore requested that information be provided as to (1) what chemicals and oils could best be used for this purpose (2) how materials used could best be introduced into the water (3) source of any other information pertinent to the subject.

        4.  The Motor Torpedo Boats of this squadron (PTs 20-30 inc. plus 42) are 77 foot, wood, planning hull boats with three 4M-2500 Packard engines, three 30 x 30 bronze propellers and three small rudders. The draft forward is about 2 feet, and aft about 4-1/2 feet. When underway the boat squats to about 18 inches more draft astern. The only source of compressed air is a small compressor of 150 pounds capacity. The maximum speed of the boats is about 45 knots, but in making night approaches, prior to attack, very slow speeds of approximately 8 or 10 knots, with one or two engines, are used.















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C.O. USS DEWEY: In spite of ideal conditions for sighting MTBs it was difficult to pick them up. In all cases discovery resulted from sighting wake and not boat.
       In view of fact that in every case wake was first sighted and not boat, it is recommended MTBs wait, engines stopped, ahead of approaching fleet and finally conduct attack using as little speed as possible.

C.O. USS ST.LOUIS: First boat located by sighting wake. The FA type Radar with which the ST.LOUIS is equipped is ineffective against such small targets as MTBs outside of about 3500 yards and is ineffective even at close range if the ship has any appreciable roll.
       MTBs should employ tactics in attacking suited to prevailing conditions such as:

1. Attack from dark side.

2. On moonlight nights avoid high speeds until attack has been made or until discovered during approach or attack.

3. Attack from downwind if possible as noise of exhausts could be heard from a distance of 3500 yards.

       MTBs should press home attacks whether or not discovered as MTBs attacking at high speeds on changing courses will be very difficult to hit.

C.O. USS PHOENIX: Motor Torpedo Boats were sighted at the following times, disclosure being as indicated:

Time Range How Disclosed
2130 4800 yards Wake
2133 4200 yards *Fired Star
2134 ? *Fired Star
2136 7400 yards Wake
2136-1/2 7300 yards *Fired Star
* Denotes torpedoes fired.

        When MTBs were on opposite headings disclosure was first noticed by their wakes and were picked up at an average range of about 6500 yards.

C.O.USS BOISE: In the vicinity of this ship no MTBs were disclosed by Radar. One was disclosed by sighting hull, two by sighting wakes. Firing torpedoes (red verys stars) disclosed two and two were seen in other ship's illumination. The sound of the motor of one boat was heard before it became visible.

CO. USS HONOLULU: The attacking MTBs were first located by their wake at about 4-000 yards.
       No sound of the motors was heard until after the boats had been sighted, and the sound was not clearly evident until the ship was abaft the beam of the boat. The wake was the most distinct feature and was sighted before the hulls were visible.

- 1 -



COMMANDER CRUISERS BATTLE FORCE: 2127 - sighted wakes of three MTBs with long glass. 2138 - sighted wake of MTB with long glass.
       Weather conditions were perfect for defense against MTBs. The sea was smooth and a bright moon was shining. In every instance the attacking MTBs were sighted by their wakes before the attack was driven home.

C.O. USS MARYLAND: The exercise was held in bright moonlight. Under the unusual conditions of visibility, the wakes of MTBs were visible at ranges up to about 5000 yards. Motor noises were detected at about 2000 yards.


Time No. Sighted Range How Observed
2143     2 4800 Wakes in Moonlight
2143     2 4800 Wakes in Moonlight


Time Event Range Located By
2131 Sighted MTB 4000 Wake
2141 Sighted MTB 7000 Wake
2148 Sighted 2 MTB Motors

C.O. USS HELENA: No original contacts were made with type FA Radar installed in this vessel. Radar ranges on MTBs already sighted were found to be accurate and reliable up to approximately 2500 yards. A few hours prior to this exercise, ranging tests of type FA Radar wave accurate results up to approximately 20,000 yards on cruiser and battleship targets.

COMMANDER BATTLE SHIPS, BATTLE FORCE: Reports indicate that the wakes were first sighted at ranges between four and seven thousand yards; in some instances the boat itself was sighted prior to sighting the wake but generally the wake first called attention to the position of the attacking boat. Radar search was unsuccessful. Only two ships equipped with search-type Radar were in the disposition.
       Upon sighting the wakes of the attacking MTBs, ships of the screen illuminated the boats and took them under fire.


- 2 -



       Operations of British on 20 August 1941 in convoying a force from Gibraltar to Malta:

0250   Presence of E Boats indicated by short flashes of light followed by sound of motors starting up. Prompt illumination by searchlight, heavily engaged by three vessels.

Noise of E Boat engine heard, immediately afterward its wake seen. Promptly illuminated, raked with Pompoms, .50 caliber and Oerliken fire.

During next 20 minutes E Boat motors heard.

E Boats difficult to see, presence disclosed when they went ahead at high speed plus visible wakes.











National Archives & Records Administration, College Park
Record Group 19, Bureau of Ships General Correspondence Files

Transcribed by RESEARCHER @ LARGE. Formatting & Comments Copyright R@L.

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