One of the many lessons learned by the Royal Navy after the Battle of Jutland (31 May 1916) was the need for better recognition signals - friendly destroyers in particular could be easily mistaken as being enemy vessels or vice versa. Within two months of the battle, details of new signals were promulgated to the Grand Fleet.
The source for this information is the file entitled Recognition Marks and Signals, Grand
Fleet 1916 in the Public Record Office (ADM 1/8464/182).
Be pleased to inform the Lords Commissioners of the Admiralty that the following are
the recognition marks and signals which will be used by vessels of the Grand Fleet only when
operating in the presence of the enemy:-
Battleships, battlecruisers, cruisers, light cruisers, flotilla leaders and destroyers will fly a special flag, 15-ft by 18-ft, of the same design as No. 1 flag, but red and yellow instead of red and white.
Light cruisers, flotilla leaders and destroyers when co-operating with the battle fleet will also display the following distinguishing marks:
A black canvas sail fills the space between the lower yard and its lifts. The foot of the sail is laced to the yard, and the sail is set by halliards fitted to the lift band. A downhaul is fitted to the head of the sail, which is furled on the yard.
Two black canvas sails are fitted, one before and one abaft the mast. They are attached
to the thwartship sail, and are hauled out to convenient positions for spreading and are furled in
the bunt of the yard.
As an alternative to the Private Signal, which is too long for use at night, the Challenge and Reply will be a succession of flashes by a powerful lamp, the flashes being either all of one colour or a combination of colours.
The special flag and day distinguishing marks will be made in the fleet forthwith.
A special lamp is required for the night signal.
The time when the signal will be most required will be during and after a fleet action, when the position of ships must be doubtful. The only powerful light now supplied is the cruiser arc lamp, but there is grave risk of this being unavailable owing to the resistances or wiring to the lamp being damaged in action, or possible failure in the 220-volt system due to damage or fuzes blowing.
A self-contained lamp is essential. The Smith's aeroplane flashing lamp is of a suitable power but it would require special fitting of coloured shades moreover it is an unnecessarily expensive article [in the original, £22 is pencilled-in] and has the drawback of a cumbersome accumulator battery and wandering leads, and is not suitable for destroyers.
...The question of the future supply of this lamp [supplied by the signal section with railway blue glass fitted] in place of cruiser arc lamps will be submitted after further experience has been gained, but at present the supply required is two lamps to every vessel attached to the Grand Fleet or which will work with the Grand Fleet in action.
Two lamps are required in order that one may be placed each side of the bridge and so be instantly ready for use.
...I urge most strongly that the supply of these lamps may be hastened to the utmost extent, and that in all respects the whole scheme be treated as most secret.
...It will be necessary that these lamps be kept as far as possible under protection and treated as secret.
They will be placed at dusk and remain in position until dawn.
Admiralty to Admiral Jellicoe, 2 August 1916:
I am commanded by My Lords Commissioners of the Admiralty to acquaint you that they have approved the arrangements for recognition marks and signals proposed by you in your letter..
Arrangements are being made for the supply of lamps as early as possible. It is hoped
that 300 lamps will be ready by the end of August, and a further 300 shortly afterwards. The
alteration in the blue glass [to railway blue] as proposed by you is being made....
Admiral Jellicoe (22 August 1916) would recommend that these lamps should be supplied to:
...all battleships, battlecruisers, [armoured] cruisers, light cruisers, seaplane carriers, flotilla
leaders, destroyers, belonging to the Grand Fleet, 3rd Battle Squadron, and Harwich Force
including destroyers of the 1st Flotilla and 4th Flotilla which may work under C-in-C Grand
Fleet but no patrol destroyers or other craft should be supplied.
CB 01246 - Grand Fleet Recognition And Signal Instructions, 1916
Issued from HMS Iron Duke 10 September 1916
The following instructions for the GFRS [Grand Fleet recognition signal] are to be brought into force on receipt of orders from the C-in-C or Flag officer conducting the operations to open the attached envelope which will contain the following order...the GFRS is then to take the place of the Private Signal at night until the signal "negative my...".
The orders to use the Signal will only be given if it is anticipated that a general action
may be expected with the High Sea Fleet or with some portion of it, and within the area
contained by latitude 53ºN and 60ºN and east of longitude 2ºWest.
Description of the Special Lamp (pattern No 4299)
To be known as the Grand Fleet Recognition Lamp, or GFR Lamp. The lamp is self-contained, producing a powerful light; by means of shades worked by stops at the side of the
lamp it is possible to make the light white, red or blue as required.
Nature of the recognition. signal
The recognition signal consists of THREE groups of lights, any combination of the white, red and blue, the first group being always a coloured group.
Each group is to consist of a series of short flashes, similar to the General Call. Three to
eight flashes should generally be used for a group and the number of flashes in a group varied to
suit the situation at the moment. It is not necessary that the pause between groups should be of
any defined length.
Two Vessels Challenging Each Other Simultaneously
Should two vessels challenge each other simultaneously, the one to the Northward
(magnetic) or due East (mag) should continue to make the Challenge; the one to the S or due W
should change her signal to the Reply.
9. IT MUST BE CLEARLY UNDERSTOOD THAT THIS RECOGNITION SIGNAL IS ONLY IN FORCE DURING THE HOURS OF DARKNESS, AND THAT THE PRIVATE SIGNAL CHALLENGE AND REPLY OBTAINED FROM THE DISC IS TO BE USED DURING THE HOURS OF DAYLIGHT.
THIS RECOGNITION SIGNAL IS ONLY TO BE EMPLOYED ON THE
OCCASIONS LAID DOWN IN PARAGRAPH 2 OF THESE INSTRUCTIONS
The following groups of lights to be used as the Challenge and the Reply in the Grand Fleet recognition signal.
First, Second and Third Day refers to the day on which the Challenge is ordered to be
used and the two succeeding days. On the Fourth, Fifth, and Sixth Days the Challenge and the
Reply for the First, Second, and Third Days respectively will be used, pending further orders:
R- RED GROUP
B- BLUE GROUP
W- WHITE GROUP
| 1st day challenge | 1st day reply | 2nd day challenge | 2nd day reply | 3rd day challenge | 3rd day reply | |
| noon - 8 pm (all times GMT) | RRB | BBR | RBB | BWR | RBR | BBR |
| 8pm - midnight | BRW | RBW | BRW | RRB | BRW | RBB |
| midnight -4am | BBR | RRB | BBR | RBW | RBW | RRB |
| 4am - noon | BWR | RWB | RWB | BRR | BRB | RBR |
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