Franklin D Roosevelt Library
The President's Secretary's File (PSF), 1933-1945
Box 59
Folder: Navy - January-June 1941




January 16, 1941.

                    THE PRESIDENT

Nine MTB's are now at Navy Yard, Washington. I asked the Squadron Commander, Lt. Caldwell, to give me a synopsis of the MTB tactics developed by his experimentation.

I found his memo on the subject very informative and considered that the President would be interested, and am, therefore, forwarding Caldwell's memo for the President's information.




Navy Yard, Washington, D.C.,
16 January 1941.


Subject           Tactical employment of Motor Torpedo Boats.

1. Considerable progress has been made by Motor Torpedo Boats toward the development of effective doctrines for torpedo attacks during daylight good visibility, in night actions, and during sudden encounters in low visibility.

(A) Daylight Attack Procedure: The attacking unit is the Squadron (12 MTB's), The battle approach is made in column formation; the standard distance between boats being 25 yards. The Squadron Commander conducts the attack, using voice radio or hand signals, since it is impossible to read signal flags down the column when making attack speed. The Squadron Commander solves the Base Torpedo Course and leads the column up to an attack point. A quick deployment is then made and when all MTB's are on the line, the order is given - "Close Throttle" - "Fire Torpedoes". (It is necessary to close throttle in order to avoid over-running the torpedoes and to give torpedoes smoother entrance into the water. It has been found possible to fire torpedoes at high speeds but the rush of water tends to act on the head of the outgoing torpedo, forcing it downward, and causing extremely deep dives.) Torpedoes are, of course, fired by Curve Fire Ahead. The Base Torpedo Course is obtained from the Sperry Torpedo Director. The torpedo tubes are trained out 10 degrees to each side, and opposite gyro angles are pre-set on the torpedoes so as to cause torpedoes to run parallel to ship's head. Torpedoes are launched from aft to forward in pair firing.

(B) Night Attack Procedure: The Squadron Commander leads the Squadron up to an attack point. Order is then given - "Attack". The individual MTB then proceeds independently to attack its particular target which has previously been designated by the Squadron Commander. (Dependent upon the number of targets, decision is made as to the number of MTB's which will concentrate on a target unit).

(C) Day Low Visibility Procedure: The mission the MTB's are carrying out will govern in conducting the attack. The Unit Commander concentrates his attack units to suit the immediate tactical situation.

2. All attacks are conducted at maximum speed of slightly over 50 knots. A smoke-laying torpedo has been developed which lays a screen 300 feet high and 50 feet wide behind which the Squadron is able to conceal its position until within the necessary effective range for the 18" torpedoes (3000 yards). A 1-degree unit of spread is used between the individual torpedoes on all attacks. This gives excellent density of torpedoes. The Sperry Torpedo Director is based upon the same principle as the Sperry Bomb Sight. It is not necessary to set target angle, target course, or target speed. A stabilized sight obtains the Base Torpedo Course quickly and accurately.

3. Extensive operations have been conducted to determine the best defense against aircraft attacks. It has been found that by making radical maneuvers at full speed (50 knots) the MTB's were able to successfully combat strafing planes and had no difficulty in avoiding bombing attacks. Machine gun camera pictures reveal that when operating in pairs the 4-twin mount, 50-caliber machine guns were extremely successful against strafing planes.

4. From the operating experience gained thus far, it is believed that the MTB is a weapon of opportunity, having characteristics which render the type suitable for multitudinous duties.


Lieutenant, U.S.N.,
Commanding, MTB Squadrons ONE & TWO.