(source: Public Record Office ADM 186/55: CB1548 German Navy Tactical Orders)
Wilhelmshaven, 25th June 1915
Gg. 2439 F. 1.
Alterations and Additions No. 185.
1. Our submarines can be recognised when on the surface by means of "Distinguishing Marks" and "Signals". At the present time the former are boldly executed recognisable marks, and consist of:-
The painting of horizontal surfaces black
The recognition flag on the conning tower, and
A white painted folding metal circle on the Forecastle.
(The Flanders boast do NOT carry these signs).
In contradistinction to British Submarines, our Submarines do not carry their numbers
painted on the conning tower. The numbers of our Submarines can only obtained by reference to
the List of Navy.
(Following paragraphs have been crossed out - Translator)
At present Recognition Signals consist chiefly of the grenade light signal B. The star recognition signal in general use by surface craft is not installed in our submarines, in view of the limited signalling facilities of our outpost boats, which do not have Recognition Key Memos on board.
Improvements of Recognition Signals for Submarines are either under trial or in course of preparation. These are:-
(1) A water-jet Morse signalling apparatus (jet about 6 m. high; water will be coloured to obtain greater visibility; it is already installed in "U.25", and is being installed in several others).
(2) Painting of figures (circles and rectangles) in special colours on the horizontal surfaces to improve recognition by aircraft.
(3) Collapsible masts on which different shapes can be carried.
(4) Fireworks of various sorts.
(5) Calcium carbide lights, to be released by submarines when submerged, these will
burn like the "Holme's Lights" of Torpedoes.
(Following is an undated manuscript correction cancelling part crossed out in original.-
The recognition signal consists of:-
(1) The grenade Light Signal B.
(2) Weissenbach's coloured fireworks.
(3) During fog, Recognition Rockets for use both on the surface and when submerged.
(The submerged firing gear is not yet in general use).
As all "Recognition Marks" and to a certain extent also "Recognition Signals" are likely to become known to the enemy sooner or later, it is quite impossible to ensure complete immunity from doubt as to the nationality of a Submarine that has been sighted.
For this reason the following instructions have been arrived at. They are based on the
principle that the preservations of the more important unit must remain the first consideration.
(1) Our Submarines, Destroyers, aeroplanes, airships and patrols are only to attack (ie fire at, depth charge, or ram) when the submarine is undoubtably hostile.
But Destroyers acting as submarine screens are to treat every submarine in their vicinity as hostile unless it is undoubtably our own.
It will, therefore, be seen that, in order to preserve our own submarines, which are especially important for our present plan of campaign, it is possible that an enemy submarine may escape being attacked.
Our submarines must avoid the possibility of doubt being thrown on their
nationality, and must make timely and abundant use of their recognition signals, etc,
whenever possible, and must show, at the same time, by their conduct that they do
not intend to attack. This lightens the task of dealing with enemy submarines.
(2) Minelayers, Cruisers and Battleships are to treat as hostile every submarine that is not undoubtably friendly immediately there is any danger that the attack of a submarine which has been sighted may be successful.
Our own Submarines must therefore avoid approaching these ships, especially when submerged, and also when on the surface they must, particularly at night and in thick weather, avoid the vicinity of our own ships, and show by their conduct that they do not intend to attack.
The regulations laid down in Recognition Signal Orders, p. 10, para. 16 for Destroyers applies in general to submarines, and must affect their actions accordingly.
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