Cdr
Alexander Mackay Scobie “Mack” Mackenzie RNVR was a senior member of Naval
Section at Bletchley Park for most of the Second World War. He led TICOM Team 4
for a few months in Germany in 1945 and returned to GC&CS/GCHQ to be part
of the History Section staying on to the early 1950s (at least). More than some other members of the section, he was
less keen simply to document what had happened at Bletchley Park and why, as to draw
out lessons that might be applicable to the National Sigint Organisation during
some future conflict.
What
follows is a short extract from the first chapter of his classified volume (HW
43/61) about the use of Sigint by the Army and Air Force (Volume XVIII of Army
and Air Force Sigint.) I’ve chosen it as it makes several timeless points: the
limitations of Sigint; how Sigint should be assessed (he uses the verb ‘appreciate’
where we would say ‘assess’) and by whom; the need for those receiving it at
commands to know that the secret intelligence they were reading came from
intercepted communications; and the limitations imposed by the strict security
regime in place. It is an antidote to the view that Sigint was (and is)
produced by an organisation able to hoover up, process, understand and
disseminate all of the communications of an adversary.
CATEGORIES
OF SPECIAL INTELLIGENCE
The
three main categories of Special Intelligence relating to the enemy armies and
air forces that became available have been classified as
"background", "strategical" and "tactical" (or
"operational"). The term "background intelligence" was used
to cover the information about the outline and detail of the whole enemy
war-making machinery which accumulated with the inflow of decrypts from day to
day, and was not only the basis for informed judgment of what might be expected
of the enemy in any given set of circumstances, but also the main source of
interpretation of new decrypts as they became available. These new decrypts,
when they appeared, took their place in the store of background intelligence
and at the same time, as productive of either strategic or tactical
information, might fall into one or both of the other categories. Strategic
Special Intelligence fed the Ministries and planning staffs with the enemy's
long-term plans and capabilities. Tactical Special Intelligence fed the
commands in the field with the enemy's intentions and provided current reports
of his operations. Any one decrypt might be productive of Special Intelligence
in any or all of these categories, but there were few that did not make some
part of background intelligence, since, in the construction of the complicated
pattern of the enemy's organisation for and behaviour in war, every item of
information was of value.
FACTORS
AFFECTING PRODUCTION
Special
Intelligence has been defined and divided into the categories in which it
became available; now, consideration must be given to the factors affecting the
production of the basic decrypt material. For any high-echelon decrypts to be
produced at all, the enemy had to use his W/T services, and these
communications had then to be intercepted by the Allies. This problem of
interception was solved to a greater or lesser degree in relation to the
positions of the original transmission of the signals and the strength of those
transmissions. Owing to the enemy's possession of the interior line in Europe,
transmissions of army and air force communications were not particularly suited
to interception by the Western Allies holding part of an outer ring, and this
produced the situation in which decryption could never provide complete access
to the enemy's communications relating to the war on land and in the air, or to
any part of it. The problem of interception therefore produced an unevenness,
detrimental to intelligence, in the cover of the enemy's communications which
was exaggerated by the next factor, the cryptanalytic problem. Here the
question was further complicated by the fact that with cryptanalysis it was not
a matter of enemy communications being readable or unreadable in the way that
they could or could not be intercepted. The success of cryptanalysis was, to some
extent, conditional. That is to say that, given time, certain enemy cyphers
yielded to cryptanalysis, while others yielded to increase in cryptanalytic
effort. This implies, of course, a system of priorities for cryptanalytic
effort, and such a system was in force in the Sigint centre throughout the war;
but, in a situation where cryptanalytic machinery was normally in short supply,
a concentration of cryptanalytic effort to produce materially more information
on any given area or subject would be certain to produce a corresponding
weakness elsewhere. At all times a balance had to be struck between the needs
of Service Ministries, which wanted everything they could get about the enemy
armed forces as a whole, and the requirements of commands in the field, who
wanted everything they could get about their own areas and matters of strategic
importance elsewhere.
The
third factor affecting the production of Special Intelligence was one of
interpretation, which could only be solved by the application of intelligence
processes to such decrypts as became available of such messages as had been intercepted.
The object in the application of these processes was to convert the decrypt
into a form in which it could be appreciated by an intelligence officer outside
the Sigint centre. The decrypted text of the enemy signal in the original
language had first to be emended into reasonable German, Italian, Japanese or
other language of origin by the removal, so far as was possible, of
corruptions, and by the expansion of abbreviations or conventional signalese. When
this had been done the original text had then to be translated into English
(usually into technical or Service English, involving knowledge of the meanings
of a large special vocabulary), and when finally the English text was available
there still remained the problems created by the enemy systems for disguising
originators, addressees, positions or intentions, or proforma introduced for
convenience in signalling.
Thus,
the access to the enemy's communications that was provided in Special
Intelligence was access only to such of his high-echelon WT communications as
could be intercepted, decrypted and interpreted. While the comprehensiveness
and sheer bulk of Special Intelligence might give an impression of complete
cover, and while its accuracy and reliability might give it a further use in
the evaluation, interpretation and direction of intelligence from other sources,
the intelligence officer had at all times to bear in mind its actual
incompleteness. It was never safe to discount evidence from other sources or
overlook possibilities on the ground that, since there was nothing in Special
Intelligence relating to a possibility, it was not worth entertaining.
FACTORS
AFFECTING USE
Such
Special Intelligence as became available, therefore, provided a literal English
version – or as literal as was possible in the circumstances – of what the
enemy was saying in his communications and such interpretation of his
statements as was necessary to make his meaning clear; and at this point, in
theory, the responsibility of the Sigint centre in the provision of Special
Intelligence ended. The product was available in its finished form, and that
form was not likely to be improved, except through a later amplification of the
information it contained.
It
remains to consider the factors affecting the use of Special Intelligence after
it became available. The first of these factors was the need for its
appreciation as evidence of the enemy's capacity or his intentions in
conjunction with evidence from other sources. Once the Special Intelligence was
available, there was no doubt as to what certain enemy authorities were saying
to each other, it remained to discover what this implied – that is to say that
although, from the point of view of Allied Intelligence, what the enemy said
was of great value, the real worth of Special Intelligence lay in what the
enemy's signals implied.
This
appreciation of Special Intelligence was, in theory, the business of the
intelligence staffs in the Ministries and at commands, it was specifically not
the business of the Sigint centre, but such was the nature of the material that
degrees of appreciation went on at all stages of interpretation, appreciation
and use, in that the better the intelligence officers handling Special Intelligence,
the more information they wrung from the decrypt while it was in their hands.
Decrypts of course possessed an almost infinite variation in the degree of
intelligence that might be hidden behind their literal translation, but apart
from hidden implication and in spite of reliability, comprehensiveness and
currency, Special Intelligence was liable to two main types of error. The
intelligence officer had to ask himself two questions. First, was the
originator of the signal stating the facts? And, secondly, what was the true
significance of the signal as decrypted? In reaching a decision on the first
question the intelligence officer had to bear in mind that the originator of
the signal might have been ignorant of the facts or distorting them for his own
purposes, so that a decrypt might be factually wrong or deliberately
misleading. It could be wrong, for example, when an air force liaison officer
was reporting on army formations, it could be misleading when an anti-aircraft
battery, reporting "no damage” after an air attack, was reporting the
condition of the battery rather than the state of the target. As to the
significance of the decrypt, an intercepted signal might only be a part of the
whole message or it might be confused with jargon or cover-names to the point
of being meaningless; or, and this was the case with the greater part of the
Special Intelligence that became available, the text in itself might be
unimportant or apparently routine, an isolated scrap of information for which
an operational or intelligence context had to be built up before it assumed any
significance at all. This problem of interpretation was dealt with by the
intelligence officer attaching such comment to the signal as he considered
necessary for its use in the next stage – its appreciation either at the
Ministries or at commands.
Dissemination
was the next factor affecting use. Once the best possible sense had been made
of the Special Intelligence available, it had to be pushed out, some part of it
to the Ministries and some part to commands. Throughout the war the handicap
imposed by communications on the use of Special Intelligence was gradually
reduced from an absolute prohibition in the Norwegian campaign of 1940 to a
situation where, in 1944, the Ministries and certain headquarters in Europe
were being fed continuously by teleprinter, and other commands, up to fifty or
so in all, through the SLU/SCU organisation. To cover the reduction of this
handicap in a few words, it can be said that in the Norwegian campaign the
comparatively small amount of Special Intelligence available could get no
farther forward than the Ministries, as no means of communication capable of
carrying material of such secrecy existed between the Ministries and commands
in Norway. In the campaign in France in 1940 Special Intelligence could be got
as far forward as British GHQ and AHQ and French GQG, but only in a disguise
calculated to give the impression that it was a series of reports from agents.
As a result, and in the general confusion of the campaign, it was never used
effectively. In the Balkan campaign of 1941 Special Intelligence reached as far
forward as the British GOC and AOC in Greece in the form of appreciations, and
by now recipients were aware of the nature of the source and had begun to
benefit from it. It was considered, in the case of GOC Crete that, in his
exposed position, Special Intelligence could only be provided under its Secret
Service disguise, and this was done on the Prime Minister's decision. It was
not until the campaigns in the Western Desert, however, that Special
Intelligence began to reach in an organised manner the commands organised to
use it, and not until the Battle of Alamein that, in the words of Brigadier
Williams, later BGS(I) 21st Army Group (who subsequently wrote a history of the
Army’s use of Ultra), Special Intelligence put Army Intelligence on the map and
"henceforward we were going to use it".
By
the date of the first of the combined landing operations in the Mediterranean
(November 1942), the arrangements for the supply of Special Intelligence to
commands in the field were being laid on as part of the normal intelligence
requirement; and with successive landings in Sicily and Italy the dissemination
of Special Intelligence developed into the organised services provided for the
landing in Normandy in 1944.
The
limitation on the use of Special Intelligence in the field imposed by the need
for security was, of course, a part and a cause of the difficulty in the
provision of adequate communications; that is to say, that dissemination to a
prospective user of Special Intelligence could be as effectively restricted by
the danger to the security of the source as by the lack of adequate
communications, and the one, the need for security, might be the cause of the
other. By 1944 the regulations governing the security of Special Intelligence
covered some eight pages of foolscap, and were the result of several years of
trial and error in the handling of the material during which it had been
discovered that the value of the source was so great, and access to it could
have been terminated so certainly by the enemy, that opportunity for effective
action that might however have exposed its true nature had constantly to be
denied to commands in the field. As an example, no direct action on Special
Intelligence was permitted unless there was a possibility, which the enemy
would consider reasonable, that the information might have become available
from lower grade Sigint or non-Sigint sources. Of course, specific action could
be taken to provide such camouflage, as, for instance, in the case of the
development of the Allied sea and air offensive against the merchant shipping
that carried military supplies to the Axis forces in North Africa. Very full
information on the shipping engaged on this traffic was available from several
sources, but the cargoes carried in individual ships and the exact routes they
would follow were known only from decrypts; other Special Intelligence at the
same time showed what commodities – fuel was usually the chief of these – were
in short supply, and as a result the Royal Navy and RAF were able to devote
attention primarily to those ships whose loss would do the enemy most harm. In
order to overcome the suspicion that might be aroused in the mind of the enemy
through the continued success of this policy of selection, it became the
practice to fly aerial reconnaissance to spot ships whose course or location at
a given time had been revealed in Special Intelligence. Once the enemy had been
made aware of this reconnaissance the information provided in Special
Intelligence as to which ships would make the most profitable target could be
used to the full.
That
these precautions were effective is shown by the fact that time and again the
right ships were sunk, and at no time did the enemy consider that his cyphering
systems were vulnerable; but the necessary restriction on the use of Special
Intelligence was severe and caused many practical difficulties. Apart from the
actual prohibition of use because the Special Intelligence was not covered by
information from a more open source, there was, certainly up to the end of
1942, the danger that the disguise of the source as an agent would have the
effect of reducing its reliability in the eyes of the recipient and so make him
less inclined to take the information provided at its actual value. Moreover,
as Brigadier Williams discovered, "once you began to pretend that it was
an agent, not only was the story highly unconvincing to those who bothered to
think about it (there were surprisingly few who did) but it entailed a
lessening of security in discussing it".
The
need for security therefore placed a double restriction on the use of Special
Intelligence in operations. Not only could disguise adopted for security
purposes lower the worth of the information in the eyes of the prospective
user, but the lack of a possible open source of the information might prohibit
its use altogether.
