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Admiral Henry T. Mayo, Commander-in-Chief, Atlantic Fleet, to the Atlantic Fleet


U. S. S. PENNSYLVANIA, Flagship.

22 March, 1917.    

From: Commander-in-Chief.

To:   Atlantic Fleet.

Subject:  Instructions governing movements of battleships in formation upon sighting hostile submarine.

     1. The surest defense against attack is speed and maneuvering ability.

     Forces shall, as a general rule, steam at their maximum sustained speed when at sea.

     At night and in thick weather course steered will usually be straight. During daylight in waters within which there is a probability that submarines may be present, if the composition, mobility and maneuvering ability of the Force permit, a zig-zag track shall be made, changing course at intervals of not more than one half hour.

     The signal to indicate sighting of a submarine shall be six short blasts on the siren followed by one long blast if to starboard and two longs b[l]asts if to port. Fire shall be opened immediately to indicates its position by splashs, as well as to sink the submarine. In ships having no siren the whistle shall be used.

     When a submarine is sighted bearing from ahead to five points on either bow and less than six thousand yards distant, the ship shall consider herself in the danger zone.

     If in the danger zone when the submarine is sighted the safest course is to head for the submarine.

     If the submarine is more than six thousand yards distant or bears further aft than three points forward of the beam the safest course is to turn away from the submarine.

     2. When in formation the following instructions shall be followed during daylight:


     Commanding Officers are authorized to turn out of column to avoid torpedoes, mines or threatened attack by submarines.

     If submarine is sighted by the leader in such a position that the ship is in the danger zone, he shall turn toward the submarine and steer directly for it until the submarine submerges its periscope, then change to a course opposite to the course steered by the submarine at the time of its disappearance.

     The second ship in column shall follow the leader until the submarine submerges, then when the leader turns, turn into a course parallel to that taken by the leader.

     The third ship, if in the danger zone, shall head for the submarine and maneuver in the manner prescribed for the leader.

     The fourth ship shall follow the third, maneuvering as specified for the second ship.

     If when a submarine is sighted the ships are not in the danger zone, they shall maneuver by pairs away from the submarine making changes of course of not more than four points at a time.

     If a submarine is sighted by a ship other than the leader of the column, the maneuvers shall be as follows:

     Leaders of pairs within the danger zone shall head for the submarine. Leaders of pairs not in the danger zone head away from the submarine making changes of course of not more than four points at a time.

     In all cases of possibility of collision the port unit shall keep clear.


     (a) Submarine sighted outboard of a flank unit. The ships of the unit nearest the submarine shall maneuvers as prescribed for column formation. Other units shall be maneuvered by signal, by the Commander of the unit, to avoid torpedo danger area.

     (b) Submarine sighted in position ahead of the formation.

         The unit toward which the submarine is heading will operate as prescribed for column formation. The other units, if any ship is in the danger zone, will turn away from the threat without signal by pairs.

     If by change ships of two units maneuver towards the submarine the ships of the port unit shall keep clear.


     No attempt will be made to maneuver except by signal. The only defense is a rapid well directed gun fire.


     During approach to, and during a major action, it is important not to break up the formation. No attempt will be made to avoid a submarine except by signal from Division Commander or higher authority.

     The Commanding Officers are authorized to change course to avoid a torpedo whose wake is clearly seen. They must regain position as soon as danger is passed.


     A Protective Scout sighting a submarine shall open fire immediately, using searchlight if at night. This is in addition to signal to be made by Very Stars.

     The scout first sighting a submarine shall follow it maneuvering to sink it by gun fire or by ramming.

     Scouts adjacent to the one first sighting a submarine shall immediately close the space left by the scout following the submarine. At night running lights shall be turned on by these two scouts to indicate their position. Running lights will be turned off when distance has been adjusted.


     A ship sighting a mine shall change course to avoid it indicating change of course by siren, sounding letter “S” if mine is to the left to starboard, and “P” is to be left to port.

     A Protective Scout sighting a mine in such as to threaten the Main body shall immediately send by radio the word “ROCK” followed by its own call letter.


     In case a battleship is torpedoed the other battleships shall be maneuvered to avoid the danger area, and shall not reduce speed until well clear.

     A division of destroyers shall be sent to the assistance of the ship struck. If the ship is not in the danger of sinking the destroyer shall use every effort to destroy the submarine.

     A ship shall be detailed to tow the injured ship if such assistance is required, joining after the area is cleared of submarines by the destroyers.

     If it is definitely known that the damage was caused by a mine the area will be searched and if necessary swept by destroyers. A ship shall be detailed to take the injured vessel in tow, if such assistance is required.

     8. A copy of these instructions shall be kept in possession of the Officer of the Deck.

/s/ H.T.Mayo.      

Source Note: Cy, DLC-MSS, William Furlong Papers, Box 4. Document identified as “CONFIDENTIAL./File 1392. 14-Ro(0)”

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