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Oo bo E!J15 ONLY 

.AFS.P..C g 13/40 

19 June 1950 

~Jl!MO:RANDUM FOR !v!EMBERS OF AFSAC : 

Subject: Replacement of the Present Combined 

Cipher Machine (COM)o 

1-> The subje@t paper is enclosed herewitn 0 and 

has been placed on the Agenda for consideration at the 

Fifteenth Meeting to be held on 19 June 1950~ 

.AFSACg 13/40 

PEARSON 

Ho De JONES 

Secreta.riat 9 AFSACo 

33 

Declassified and approved for release by NSA on 09-20-2013 pursuantto E .0. 1352a 

. £USotll TOP SECRET \t S.- 1; 
. - ~F,, ~:g .. =.~~.35986. 

~ .~} ~; ~~~} ~u·, :~~~ ~ ·~ /.~~ ~ 

B!fOR'l' BI THE -~g~o FQEGEB~~5t:..::~L-~9!4r~QLS&.YJIQ.ll 

~ 

VIA '1'.HE .JOINT COMivJfJNICATIONS~~ELEGTRPrGm:i l~OVf1.:ll l~T.EE ... -=-· --.. =-= ......_ .... ~ .. ~==-==::=;;=-~=-~ 

to the 

JOINT CHIEFS ~=-~ OF' STA.1F 

T"'.dE PROBLEM 

3S 

to the memorandum by the Represtmtutives o:f' the D:i.."it.ish Chieff.J of 

Staff 9 RDC l/46 dated 14 Februa1~y 1950 (JCS 2074/3) regarding the 

feasibility of constructing an adaptor tor u,,s.~ u::;:n whieh ·:J.:i.11 per= 

mit in.teroo.m.l.imnication v11i·Gh the con.tem.ple.ted new :31.,iti.sh. ctpher 

machine a 

2q See Enclosure "B~~ o 

CON9LUSIONS 

Jo It is concluded thut: 

ao While there is no doubt that the BrlM.sJj are aware oj".' the = 

basic important ECM prix:iJ:::d.ples t1 and propose to ineorpore:.\f::;e them :Lu 

a new British cipher machine 9 they apparer.i.tly lac.i~ consid~: .. :Elble cle= 

tailed ·knowledge concerning our specifi~ applicat~~.cu1 or th<1se 

principles in the ECMo 

.2,o To adapt the proposed British clpher mach·~.r:.e t,o use for 

the EC/II which they now lacks and. wcmlc1 require to y;,:vduc0 a machl.no 

practically equi v&.lent to ouz- EC Mo 

=l= 

Declassified and approved for release by NSA on 11-19-2013 pursuant to E .0. 1352a 

U. S. EYES ONLY 
9TOP 

Jt ~umy~ QNL¥ 

£~ The replacement for the CCM9 to be agreed upon by the UoSo~ 

U o Ko" may'_laterf.J especially in wartime 11 have to be used also by allied 

British Dominions 9 particularly Canada 9 and possibly by other allied 

countries a 

~a The UoSo~ as a matter of policyp should not disclose to any 

foreign country the complete details of the ECM, even thou~h tech= 

nicHl considerations might favor the use of the ECM for combined 

communications'J 

~o While the proposed British cipher machine would be adequately 

secure for hi~hest=level co.m.munications 9 . development 9 · refinement and 

procurement of such a ma.chine by the agreed date for replacement 

(l January 1955) is extremely doubtfulo 

!o The UoSo has current need 9 without considering combined 

needs 9 for more than one cipher machine afrording adequate security 

for highest level communicationso. 

~o The UoSo should propose to disclose to the British experts 

a working moa.eJl. of the 7-rotor BCM for consideration as replacement 

for the present CCM0 in lieu of further consideration of adapting 

the contemplated British machine for combined UoSo~UoKo usea 

,ho The U"S" should also disclose to British experts a working 

model of· the PCM when availableo 

.!," In addition to a replacement for the present CCM9 the U oS., 

and British Navies have an urgent requirement in combined communi= 

cations for a secure small cipher machine = particularly for sub~ 

marinesp certain surface ships 9 and for large fast merchant shipso 

lo Comparable British ana UoSo cipher machin~ whenever prac~ 

ticablev should use physically interohangeeble rotorso 

RECOMMENDATION.§. 

4o It is recommended that: 

_,, 

ao No further consideration be given to using the ECM prin~ 

ciple for combined communicationso 

TOP SECRET 
e 

U. S. EYES ONLY T O P 

~:E" -~r:g :~_435•6 SEC i( E-~ .... 

. .:20 7-rotor BCM and lightweight versionp PCMr. working models 

be disclosed in 7/ashington by the U !>So to the British for conai-= 

deratiori as the replacement for the CCMo 

£0 The UoSo reply to t4e British be as set Torth in 

Enclosure "A" o 

-\l. S. l1lS \ll\1- ·roP SECRET 
e 

TOP 

REF ID:A2435~6 

SECREl- • 

~.w.r:ORA.tJDUU FOH T!lli REl'RLSr~l'!Trl. 1'IVES OF THE BRITISH C'RIE!t'S OF STAFF 

lo The Uo s. Chiera or Staff have had a thorough study made 

of' the drawings Of the proposed new British cipher maohine 11.h,ioh 

were submitted as an enclosure to RDO 1/48 of 12 April 19500 It· 

has thus been ascertained that the proposed new British machine 

should be secure for highest level oomm.unioations, and that a 

Uo So cipher machine probably could be adapted to rermit inter~ 

oommunication~ However, a worldng- model would be required in 

order to determine the practical reasibility or such adaptationo 

2o Because of the time wbioh experience indicates is re= 

quired to develop, refine~ and procure a new cipher machine» such 

' 

as the UaKo ha~ proposedg and because of imp~rtant technical and 

poliay considerations, instead of further oonsiderine the adap0 

te.tion of the propo,aed new British machinefl the U-0 So Chiefs of 

Start propose that as the lone-t.erm solution ot a replacement 

tor the present combined c1pher.maah1ne (COM}, cons1derat1on be 

given to the ?orotor BCMo 

3o The u6 So now has a working model or a ?=rotor BCM 

available tor examination 1n Washington bf British cipher machine 

experts 0 if the British Chiefs of Statt are willing to consider 

the adoption ot auoh a machine as replacement for the CCMo The 

Uo So expects also to have available tor examination a smaller 

lighter-weieht working model of the ?=rotor BCM (termed the PCM) 

berore the end. ot calendar year 19500. This machine has been 

developed primarily for tuture ·.Naval useo The ?=rotor BC:M/PCM 

can readily be. adapted to intercommunicate with the present CCMo 

4o The Uo So 7=rotor BCM/l'CM proposal tor combined UaSo~U.Ko 

oommunioations has taken into consideration the necessity not only 

tor providing security tor highest-level command combined oommuni= 

U. S. ElES ONL\ 

TOP SECRET 

4 
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cations, but also for communications in combined operating forceso 

The u. s. Chiets or Staff concur with the British Chiefs of Starr 

in wishine to avoid having numerous operating units (especially 

ships) enc.umbered with. more than one type of cipher machineo 

So The security to be af:f~rded by the 7 ... rotor BCfl (Fer!:) 

is considered to be of a bo·ut the same high order as the u o ~o E~M 

and the proposed new British ma9hineo 

60 The Uo So Chiefs ot Staff further propose that 9 so tar as 

praotioablep comparable British and Uo So cipher machines use 

ph.yeioally interchangeable rotorso The 7-rotor BCM rotors are of 

the sallle size as those in the COM (CSP 1700)0 Such standardization 

would permit eme~gency issue of rotors by ei-ther country to the 

other, 11' neoes·sa.ry o 

?o If the UoSocU.K., agree on the 7c:>rotor BCM (PCM) as the 

new combined cipher maoh1ne 0 the UoKo would not have to undertake 

extensive time-consuming development work 0 and 0 it desired, could 

probably expedite procurement by combining procurement orderaQ 

It is anticipated that the replacement date (1 January 1955) can 

be met 1f the ?=rotor BCM (PCM) is agreed upon as the replacement 

ror. the CC.M; the ?=rotor .BCM (PC?•O. would be less complex in construction than the proposed British maohine 0 and moet of the parts 

have already proven satisracto:ry in actual uaeo 

s 

u. s. Ettti Uhtl TOP SECRET 
•- ~-E? __ ~1--~~ e>Rf?:f3si6 ~Thie ONLY 

l::fJCLOSllRE "B" 

FACTS Bi:;AHING OTJ l'HC. PiiOBLBf;i AND DitiCUSSION 

lo l'.'hile this p;iper pertains to u.s.-UoK• COlil!Jlunications, it should 

be understood that the combined cipher machine to be agreed upon for 

U.So~U.K. communications may later have to be made available for use 

also by allied British Dominions, ~specially Canada, and possibly also 

by other allied c oo.ntrie s. 

2o In JCS 2074, one of the conclusions of the U.S. Joint Chiefs of 

Staff was 9 "the release of the BCM under present circumstances is not 

warranted." Instead, JCS 2074 proposed, for combined use, a UoSo 

machine, the 5-rotor BCM. This ma.chino was subsequently di~closed to 

the British and rejected on the grounds that a 5•rotor cipher machine 

would not be sufficiently secure as a long~term solution. 

3. In RDC 5/99 dated 13 July 1949, the British Chiefs of Staf£ 

continued to express concern regardine; the security of the present 

combined cipher machine on a long-term basis and stated: 

.!• That they had decided to replace their main cipher machine 

(TYPEX) as soon as possibleo 

~· That they felt it necessary to have a single machine which 

would be able to provide both intra-British communications and 

combined UoS.~British communicationso 

~· That they requested the UoS. Chiefs of Staff to authorize 

the disclosure to the U.K •. cryptographers of the principles and 

details of the .&;CI.I so that these r1light be incorporated in the 

contemplated new British machine. 

4. In JCS 2074/2 dated 10 January 1950, the U.S. Chiefs of Staff 

denied the British request £or principles and details o.f the EGr·'I9 

but indicated two possible alternative solutions: 

ao Solution A. Disclosw.·e by the UoKo of a copy of its con00 

- ternpla t.ed new cipher machine, or detailed drawings thereof» so 

that the UoSo could ascertain the feasibility of constructinz 

ari adaptor for U.S. use ~mich would provide the basis for secure 

combined comu1unications by utilizing the new British machine 11 

when available 9 and an existing UoSe machine with an adaptoro - . -· ... :-- -

U. S. EYES ONLY TOP SECl<ET 

i'OP S§@RBf tJ. S. El1;! S ONLX ... 6 = 

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l?.• Solution D. The possibility of usins a 7-rotor Beil which 

th a U .s. was developing. 

These alternative eolutions are -discussed in paragraphs 5 and 6 

below. 

5. SOLUTION A: 

~· The drawint;s of the contemplated ne\~ British cipher machine 

(Enclosure to JCS 2074/4 dated 13 April 1950) have been received 

and confirm the statement of the British Chiefs of Staff in 

Para. 6(b) of RDC 1/36 (Enclosure to JCS 2074/l, dated 6 December 

i949) that ·the new Dritish :machine would be built to operate on 

the broad principles of the ECMa . 

b. The British security evaluation or their contemplated new - machine is sound; the resistance of the machine to cryptanalysis 

should be a~ least as great as that of the BCM and hence would 

be a~equately secure for highest-level communica'oions.o 

~~ It can be deduced from the drawings that the UoKo has not 

yet built a workinz_model of the new Dritish raachine 9 and, therefore, while the U.K.' still has full latitude in the determination 

of certain details of basic construction, it is several years 

away from the procurement stage. 

£e Although the contemplated new British machine will·a~body 

the basic princ;Lples of the hCM, there are significant differences in detailed application of the ECM principles. As a 

consequence, ~n order to make the two machines intercommunicable~ 

it would be necessary for the u.s. to-provide the British with 

certain detailed information applicable specifically to the ECN • 

.!• The provis~on to the British of detailed information about 

the ECM would not be necessary for the use of their new machine 

for purely British intra-comruunication. 

fo If th~ Dritish are provided with required detailed LC!vl 

in.formation, the security oi' the resulting .coiabined system would 

be of the same high order as that of the ECI·l· 

~Q As regards the effects on our own commun1ca tion ·security !l 

Qf the disclosure ~o the British ot tha detailed informt.ion 

U. ~- _ttES ONLt T O p S E C R ET 

'.t'OP S:LiSii-J:i! 0 YaS •. BY.i!iS ONliY ..,. 7 = 
referred to above, there probably would be no change in the security evaluat.ion oft.he .r..CM. Although the U.d. has always emphasized the .importance of the physical security of our cipher m9.chinesm 

our evaluation o.£ the bCll is predicated on possi 'ble ultimate enemy 

possession of the LCI·l machine,, and our security is based upon 

regularly changing the rotors and key listso The privacy or U.S. 

communications against cryptanalytic attack by any foreign power, 

including the British, could be assured. 

!l• If the British were to include in their new machine appropriate wiring, based on detailed ECM: in.formation supplied by the 

U oS., security fer intra-British communications would not be af ... 

fected, and if certain special rotors were used by them, a rela• 

ti vely sir.iple met hod of use of the ~CM by the U.S. with one 

special rotor per r.iachine would permit inter-com1.1unication between 

the proposed new British machine and the U.S. machine o 

.!• The cost to the U .;:>. ol' the adoption of t.his solution would 

be less than ~1 000,000 and an existing U.S. machine (.t;CI~I} could 

be used fer u.s.-u.K. combined communicationso 

Jo Present UoS• procedure in the use of the bC~! could remain 

uncbtinged, except £or use of a special adaptor rotora 

~· The UoKo would have to use at least four special adaptor 

rotors 9 which would very slightly reduce the security of the 

British machine, but not sufficiently to cause any concer~o 

,!o The great disadvantai?e of Solution A would be the loss of 

the f'ull CQntrol of the .E.CI·I which we have_ al·ways regarded as 

vitally important to the u.s. 

6.. SOLL''f!ON B: 

!.• A model of the 7-rotor BCM is now available and can be 

shown to the British experts in 1·Jashington with a view to holding discussions regarding its adoption f.'or. combined communica.,,. 

tionso In this connection, certain points shou.ld be considered =-

namely: 

(1) The British desire to provide but one cipher 1aachine 

£or their own internal use as well as for combined useo 

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' ' 

(2) We can adapt the .i:.CH to ·work \·tith the 7-rotor BCI.-1, and 

the 7-rotor BCI•I to work ·with the· present CC.i."i• The present CClI 

will probably be in use for several years to come tb- even 

though. the U.S. and u.r. replace the present CCI•I for corJbined 

(3) A 7-rotor BCI·I sh-ould assure the u.s.-u.K. of the highest""' 

level communications security on a long•term basis. 

~· JCS 2074 stated that the means and methods employed for the 

protection of U.S. comr.o.unications constitute a private matter not 

to be shared in toto with any other government, and that the UoS. 

must reserve for itself a cipher equipment 0£ assured security to 

provide· privacy for its own coIIllllunications.. Although it is now 

clear that the Dritish understand the basic important principles 

of our ECI•I, and intend to incorporate them in their new machine,. 

they lack important specific information concernine; applications 

of these principles. As a matter of National policy 9 - it is 

therefore considered proper not·to disclose furtheJ" details of 

the ECM to any Loreign country. 

~o Continuation of this policy appears desirable for the 

reason that by sharing the ECI<i, we lose much of the existing 

full control over this vital machine. Such full control: - ( 1) Permits us to enforce measures. to insure the physical 

security of all ele&11ents of the rnachine against. loss or compromise, by limiting distribution and pre$cribing adequate 

.safeguards o 

(2) Permits us full freedom to apply modi.fications when 

desired' to enhance our communication security. 

(3) Affords us maximum ass"Urance that; no foreign nation 

that might try· t·o read our messages will have possession of 

one of our machines, which possession mir;ht permit a moi .. e 

direct attack (by cryptanalysts) by revealing det.aj.ls or 

:r.todifi cations not already :known o However 9 our cryptan~lysts 

beiieve that such attack ·woul~ not .be successful unless the 

fore·ign nation concerned possessed also our rotors and key 

11sts 0 which are regardec;i as more vital security elements 

than the machine chassis • 

. . 

U. S~ · E¥ES DNlY TOP SECRET 

fOP StiOH§f ; ;J4 .. S. #JES OiUZf ... ""' Iii.... .... . . •.' . 
.S,o £;xperience to date indicates that neither the :3ritish nor 

the U .s. can develop9 refine and produce a reliable completelye.new 

cipher machine in le~s than five yearso Therefore 9 the U.Llo will 

probably have to of£er the British a U.So=developed cipher machine 

if the target date of 1January1955p.which has been agreed upon as 

the replacement date for the present CCM9 is to be met o 

,!o It is believed that the British!) when sho-wn a work:i.ng model 

of the relatively less complex but "highly s~cure 7-i"otor DCI•i~· ·will 

abandon their own proposed development and will accept the 7•rotor 

BCN as the replacement for the present CCN as t'l!Sll as for their O't'm 

intra 0 British use6 It can surely be refined and produced in less 

than f':i.ve ( 5) years 9 if funds therefor are provided9 (approximately 

~6v000 000 for the U.So) because most of the parts have already 

proven satisfactory in actual useo 

£0 In addition to the problem of imp~ovine the security of 

highest=level combined con1.1unicationsll there is the current 

problera of providing improvedti adequately-=-secure crypto systems 

for U.So and U.,Ko operatin~ force use 8 especially in: 

(1) Merchant shipso 

(2) Amphibious crafto 

(3) Submarineso 

(4) Patrol crafto 

,&o Since 1944 the U.S. Navy has had under development a snali 

lightweight cipher machine (the PCM) to fill Ne.vy requirement.so 

The PCM will be cryptographically identical \'Jith the ?=rotor l3C1'1 9 

and should be suitable for large and small ships~ It is expected 

that the first development model of the PCM will be completed 

about Uovember 19500 Both the PCI<l and 7.,..rotor DCf.1 will have pro~ 

vision for int ercorcmunicating with the present CCM and ECI•lo 

ho The logistical problem of secure combineq. collmunications 

is of much ereater magnitude and complexity for the Navies conQ 

earned than f'or the respective Arr.1ies and Air Forceso For ex"" 

~ple, dur·ing liorld \1ar Il 9 the U .3 o Navy procured and used 

a.bout 15 times as uany CCNs as the U "~"' Army and Air Horce 

combined 9 even though the CCM distribution \~as limited t.o 

"l:li.a.jor ~;ar Vessels" (destroyers and larger)o 

•.10""' 
• r • ~ - - • - REF.D :n4i5flae6 E c R E-f0~1& £JiS.,1lNl],e;, eYLS OHL-Y·-· ··--· - ... -··· 

7. FAC'fD APPLICAdL~ TO 1301'II SOLU1'ION A A:m 50LU:.rroi~ B: ' ..... 

!.• A machine of improved security would have to be issued to 

those U .s. commands froo whom the ECI-1 was ·withdrawn in 1947 in 

~ensitive overseas areas. 

S.o 'rhe e.ff'ect upon the communication intelli~ence interests 

of the u.s. either durine the present world situation or during 

actual hostilities, would be the same. If used by a foreign 

country, either proposed uachine, for all practical purposes, 

would be unbreakable by the U.S • 

.£• Lxpet·ience has demonstrated that the- emergency issue of 

rotors by one country to the other is of considerable practical 

value. If' British machines are designed to use the same size 

rotors as thosa used in comparable U.S. machines, such emergency 

issue would be greatly £acilitat~d. 

~o Althoueh the cost to the U.S. in solving the illll:lediate 

high level combined problera would be substantially larger under 

Solution B, the total over-all cost to the u.s. Government {par~ 

ticularly because of the special Naval requirements referred to - ' -. 

in Paragraph X·! .. , which are combi~ed as well as intra-UoS.o Navy 

requirements) would· be essentially the same under either solutiono 

This total cost camot be closely· estimated pending completion of 

certain cipher• projects still under developmento 

S.· The u.sD has already agreed t~~t, if.necessary~ we wi.11 

provide the British with a limited number of adequately-secure 

cipher machines -(from U.S. stocks) to meet an emergency: si-tuation 

which mi@lt arise before 1 January 1955 when the replacement CCM 

is to be a vai lab le • Which U.S. machine this· will be depends upon 

the then-existing circumstancesa 

U. S. [1tS OHll TOP SECRET 

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