Register No. 1


CSP 493


Navy Department Seal


Declassified, Authority NND 003 004, by R.T. 3-17-05



CSP 493

Washington, D. C., October 15, 1926.


1. This publication (CSP 493) and the Cylindrical Cipher Device (CSP 488) are confidential, and will be handled in accordance with United States Navy Regulations. Report of their receipt, transfer, loss, compromise or destruction, and semiannual return will be made to the Chief of Naval Operations (Registered Publication Section).

2. This publication will be bound in weighted cover for naval ciphers (CSP 100). When necessary to be given to landing force for use on shore, it shall be temporarily removed from the weighted cover.

3. No officer shall attempt to use the Cylindrical Cipher Device until he has read this publication and thoroughly understands the instructions contained herein.

4. The distributions of this publication and of the Cylindrical Cipher Device are in accordance with the current issue of "R. P. S. Distribution and Allowances."

5. These instructions, and the Cylindrical Cipher Device will become effective upon receipt.

6. Comments and criticism on this publication, and suggestions for the improvement of the Cylindrical Cipher Device or these instructions should be forwarded to Chief of Naval Operations (Code and Signal Section).

Admiral, U. S. Navy,
Chief of Naval Operations.

Part I

1. The cylindrical cipher device (CSP488) is a mechanical means for enciphering plain language messages. Its operation is simple and fairly rapid; its security against cryptanalysis is relatively high.

2. The naval use of the cylindrical cipher device is fourfold:

(a) For intercommunication between the Army and the Navy. (See CSP494.)

Note.-The United States Army has an identical device (M-94) which has been in use since 1921.

(b) For communication between Marine Corps or naval units in the field, or between ships and units of a landing force.

(c) For use as a naval district cipher.

(d) For use within the fleet, including fleet maneuvers, when so prescribed.

3. With a knowledge of the mechanical operation of the cylindrical cipher device, there is required to put it in operation, nothing further than the mental possession of the current "key word," or "key phrase."

4. (a) The key word for Army-Navy secret intercommunication is determined as indicated in paragraph 12 of CSP494 (Instructions for Secret Intercommunication between the Army and the Navy).

(b) The key word for use in connection with landing force activities or Marine Corps units in the field is designated by the senior naval or Marine Corps officer present.

(c) The key word for use in naval district activities is designated by each district commandant.

(d) The key word for use within the fleet, or subdivisions thereof, will be prescribed by the officer in command of the unit in which the cipher is to be used; if the use of the cipher is also required by naval units beyond his command, he will take steps to furnish the key word to such units. In the case of extensive fleet problems, where the use of this cipher must be known to many units on shore, the Chief of Naval Operations will, upon request, designate the key word and send it out to all units involved.



Part II

1. The cylindrical cipher device is made of aluminum, and consists of a shaft upon which are mounted 25 movable alphabet disks held together by two end pieces and a thumb nut screwed on to the threaded end of the shaft. To the rim of the left end piece is attached a straightedge which, when the device is assembled, lies parallel to the shaft and flush with the periphery of the alphabet disks. The right end piece is stamped with the words "US NAVY CSP 488."

2. On the periphery of each one of the 25 alphabet disks is stamped one disarranged alpha- bet; each of the 25 alphabets is differently mixed. Each alphabet (i.e., each disk), is identified by a number (1 to 25) and a letter (B to Z), stamped on the cup surface of the disk. This letter and number can be seen only by disassembling the device, i.e., taking the disks off the shaft. (Either the letter or the number may be used in setting the device for the key word or key phrase. For the present, only the number is prescribed for use.) The alphabet disks are interlocked, to prevent rotating. relative to each other, by means of a lug on the cup surface (right hand side) of each disk and a rack on the plane surface (left hand side) of the adjacent disk.


Part III

1. The cipher key.-In order to use the cylindrical cipher device it is first necessary to assemble the disks on the shaft in a certain sequence which is determined by the key word or key phrase. The key word or key phrase to be used will be designated as indicated in paragraph 4, Part I, and should be at least 15 letters in length:

2. To set the key.-(a) Unscrew the thumb nut and remove the right end piece and all alphabet disks from the shaft. (Leave the end piece to which is attached the straightedge, on the shaft.) Lay all disks on their plane sides, identifying marks up, and in their numerical order from 1 to 25. (In these instructions the disks will be identified by their numbers rather than their letters.)

(b) Write the series of numbers 1 to 25 equally spaced in a horizontal line on a sheet of paper, and then write the letters of the key word or key phrase beneath these numbers, repeating if necessary, until a letter is below the number 25. (If a key phrase consists of more than 25 letters, the letters beyond the twenty-fifth will be disregarded.) For example, using the key phrase, GENERAL ELECTRIC COMPANY, write thus:

1 2 3 4 5 6 7   8 9 10 11 12 13 14 15   16 17 18 19 20 21 22   23 24 25
G E N E R A L   E L E C T R I C   C O M P A N Y   G E N

(c) Now proceed to place numbers under these letters, starting with number 1 under the first letter of the alphabet that appears, i. e., under the first A put number 1; under subsequent A's (if there are any more in the key phrase) put number 2, 3, etc.; under the next letter of the alphabet that occurs, put the next consecutive number; and so on, always making the inspection of the letters from left to right thus:

1 2 3 4 5 6 7   8 9 10 11 12 13 14 15   16 17 18 19 20 21 22   23 24 25
G E N E R A L   E L E C T R I C   C O M P A N Y   G E N
  6, etc.   1       3   4   5   2

Continue until all letters have been assigned a number (25 will be the last number). The example above will then appear completed thus:

1 2 3 4 5 6 7   8 9 10 11 12 13 14 15   16 17 18 19 20 21 22   23 24 25
G E N E R A L   E L E C T R I C   C O M P A N Y   G E N
11 6 17 7 22 1 14   8 15 9 3 24 23 13 4   5 20 16 21 2 18 25   12 10 19

This sequence of numbers 11-6-17-7, etc., is the order in which the alphabet disks are placed upon the shaft; that is, disk No. 11 is placed first on the shaft (cup side toward threaded end of shaft); disk No. 6 next; disk No. 17 next, and so on. When the last alphabet disk (No. 19 in the given example) has been placed on the shaft, put on the right end piece and screw down the thumb nut lightly to prevent disks slipping off the shaft in handling. The instrument is now set up ready for use either for enciphering or deciphering messages.

The instructions for setting the "Key" must be thoroughly understood and accurately followed, since the operation of the device is wholly dependent on the proper key setting.

3. To encipher a dispatch.-(a) Having set the cipher key as indicated in paragraph above, back off the thumb nut about one-fourth inch, and by revolving each alphabet disk until the proper letter comes up, spell out along a continuous line from left to right the plain language of your message. The straightedge will be found convenient for marking the line upon which the letters of the message are being set. Having lined up the disks so that they spell out the first 25 letters of the message, and having engaged them with each other, now separate the first (left) disk from the end piece, and, holding the rest of the cylinder firmly, rotate the end piece until the straightedge is on any line (except the one immediately above or below) above or below the line on which appears the plain language message.

Caution: With the thumb screw loosened in order to rotate the straight edge, be careful not to disengage any of the alphabet disks from their engaged position in relation to each other.

A line having been selected at random, lock the device by screwing down the thumb nut. Now write down, in groups of five, the letters in the line selected (the notches on the straightedge indicate the division of the line of letters into groups of five). These five groups will be the cipher equivalent for the first 25 letters of the plain language message.

(b) The next 25 letters of the message are enciphered by repeating the operation explained in (a), i.e., the twenty-sixth letter of the message is set up on the first (left) alphabet disk, etc. Continue this operation until the entire message has been set up, each 25 letters requiring the complete operation explained in (a).

Caution: Select a different encipherment line at random for each set-up of plain language.

When the total number of plain language letters in the dispatch is not a multiple of 5, the last group will be incomplete and must be filled out by adding letters that are plainly nulls.

(c). Whenever numbers occur in a dispatch they must be spelled out. For example:

"Hill 608" would be enciphered "Hill six zero eight."
"6th division" would be enciphered "sixth division."

Note.-It is not necessary to make a record of, nor to indicate in any way whatever in the dispatch, the lines from which the cipher was taken.

(d) For cryptographic reasons, the use of abbreviations is encouraged, provided that the garble of any one letter in the abbreviation is not likely to invalidate the sense of the message.

(e) As differentiated from the 10 group minimum prescribed for code messages, in the use of the cylindrical cipher device no required minimum is placed on the number of groups com- posing an enciphered message. For cryptographic reasons, the use of dummy words or groups for any purpose with this cipher device is forbidden.

4. To decipher a despatch.-Knowing the key word or phrase, and having arranged the disks in correct sequence as explained in paragraph 2, Part III, set up the first 25 letters of the enciphered despatch along a continuous line from left to right. Now disengage the left end piece and revolve the straightedge slowly until you find the line which reads intelligible text. There will be no difficulty whatever in finding this line, for it will be the only one which yields coherent words. This will be the plain text for the first 25 letters of the despatch. Now set up the next 25 letters and pick out the plain language in the same manner; and so on until the entire despatch has been deciphered.


Part IV

1. Where it is necessary to have these instructions in the field, they shall be kept at head-quarters where their proper safeguarding can be assured.

2. The security of this cipher depends entirely upon the secrecy of the key word or key phrase. The key word or key phrase prescribed should be memorized, together with the method of deriving the key setting from it.

3. The key phrase effective should be changed at frequent intervals, the frequency being dependent on the amount of traffic that has been sent with this cipher.

4. In enciphering, never take for the cipher either the line immediately above or below the plain text, but select the lines of cipher in a very irregular manner from any of the other 23 possible lines. In addition to selecting at random a different line for the cipher of each single set-up of plain language in any one message, never use the same initial lines or order of lines in successive messages.

5. When in imminent danger of capture, remove all alphabet disks and mix them up thoroughly.


Part V

1. The prospective operator will find the following problems and solutions of enciphering and deciphering with the cylindrical cipher device a convenient test of his familiarity with the methods explained in these instructions.

2. (a) Using the key phrase, "John Quincy Adams," encipher the following despatch:

"Landed on beach No. 6 at 0510 without casualties."

One correct encipherment of this despatch is the following:


(b) Using the key phrase, "Naval District Cipher," decipher the following despatch:


The plain text of this despatch is:

"Request boat for casualties."

NOTE.-Whenever conditions permit, the operator should always verify the encipherment by deciphering the completed cryptogram.

From US NARA College Park: RG 38, CNSG Crane Library Box 33

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