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S.P. 02201
Signalling Instructions · 1935

S.P. 02201 is the reference number of a set of Signalling Instructions for encoding and decoding messages, issued by the Admiralty of the British Navy on 1 October 1935. The instructions are divided over four parts, of which Part I and IV are bundled in the book shown in the image below. In the context of this section of the website, it is considered to be a procedural codebook.

The book is marked CONFIDENTIAL and contains references to penalties under the Official Secrets Acts, if confidentiality is not respected. For this reason, each copy is numbered individually. The copy shown here has serial number 6158 [1].

According to a note on the first page, the cover is weighted with led, to ensure that the book will sink when thrown overboard. The book is signed by Sir Oswyn Murray 1 of the Admiralty, with strict instructions that every precaution had to be taken to ensure that the book - and any other signal book – would not fall into enemy hands.
Front cover

It contains detailed instruction on how to create a message, with the appropriate fields in its pre­amble, such as the time of origin (TOO), the addressee and the recipient. It provides instructions for coding and decoding, sending status and weather reports, and for giving each message the desired priority. As with all Naval instructions, the procedures are worked out to the finest detail.

When security was compromised, the codebook had to be destroyed immediately, so that it could not fall into enemy hands. The preferred method for this was to destroy it by means of fire. The alternative method, if no fire was at hand, was to throw it overboard. As the covers of the book are filled with thick lead panels, the added weight will cause it to sink immediately.

The book was introduced to the British Navy in 1935, and was used during WWII, as indicated by the many corrections and inlays that were added during 1943 and in particular 1944. It was also used by the Dutch Navy (Koninklijke Marine), which was the only part of the Dutch Department of Defense that was fully operational whilst, during WWII, the country was under German occupation.

  1. Sir Oswyn Alexander Ruthven Murray GCB (17 August 1873 - 10 July 1936) was a British civil servant who spent most of his career at the Admiralty, serving as Permanent Secretary from 1917 to 1936.  Wikipedia

  1. General Signalling Instructions
  2. Visual Signalling Instructions (O.U. 5366) 1
  3. Wireless Signalling Instructions (S.P. 2203) 1
  4. Coding and L/T Instructions
  1. Issued separately.

S.P. 02201 Signalling Instructions - Codebook with lead cover, used by the Dutch navy Front cover Peeking at the first page Murray's signature First page with inlay Corrections Detail Abbreviations
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S.P. 02201 Signalling Instructions - Codebook with lead cover, used by the Dutch navy
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Front cover
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Peeking at the first page
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Murray's signature
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First page with inlay
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The following expressions and abbreviations are used in the book. They are listed in Chapter I — Technical Definitions, and the user is assumed to be familiar with them when using the book.

L/T   Line Telecommunications
All methods if communication by land line or submarine cable, including telephone, teleprinter and Morse telegraphy.
P/L   Plain Language
Any recognised language used for a message, whereby the meaning is intelligible without the assistance of a decode (or decypher).
R/T   Radio Telephony
Method of passing speech by means of electro-magnetic waves which can only be rendered perceptible by electrical devices.
S/S   Sound Signalling
Method of passing message in morse code by means of a siren, fighorn or whistle.
S/T   Sonic Telegraphy
Method of passing morse signals through the water by means of sonic waves.
V/S   Visual Signalling
Communication of message by sight. This includes gestures, flag signals and sometimes also Sound Signalling (S/S).
W/T   Wireless Telegraphy
Communication of the message by electro-magnetic waves, or by sonic waves through the water (S/T). Messages sent by W/T, R/T or S/T are therefore all regarded as W/T messages.
THI   Time of Handling In
The time at which a message is handed over to a Cable or Telegraph office for transmission by L/T or Commercial W/T. It appears on the delivery copies of these messages.
TOD   Time of Despatch
The time at which the transmitting ship clear a message. In messages to more than one receiving ship there may be more than one TOD.
TOO   Time of Origin
The time at which a message is authorised, except in F/F and Enemy reports, whe, in the absence of a definite statement to the contrary, it is the time at which the occurence forming the subject of the report was actually observed.
TOR   Time of Receipt
The time at which the receiving ship completes the receptionof the message.
  1. Anonymous, S.P. 02201 Signalling Instructions Part I and IV
    Retrieved October 2010.
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Crypto Museum. Created: Saturday 08 July 2017. Last changed: Friday, 23 February 2018 - 22:00 CET.
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