The document provides an overview and summary of J.C. Masterman's book "The Double Cross System in the War of 1939 to 1945". It discusses how: 1) The British developed an elaborate double-agent system during World War II to gather intelligence from Nazi Germany and mislead their plans. 2) Early double agents like "Snow" demonstrated the challenges of ensuring agent loyalty and managing communications with the enemy. 3) The double-cross system evolved and proved hugely successful, particularly in influencing Germany's response to the D-Day invasion in a way that contributed to the Allied victory. 4) While Germany proved capable, factors like Britain's impartial intelligence service and the inherent uncertainties of esp

1. The Double-Cross System: Lessons in Deception and Shifting Loyalties
A Review of J.C. Masterman’s The Double Cross System in the War of 1939 to 1945
by Nicholas Arciniegas
“A live spy, even if he cannot transmit messages,
is always of some use as a book of reference. A dead
spy is of no sort of use.”
The field of intelligence is largely an exercise in deception--a game in which its primary
players attempt to collect intelligence through obfuscation, manipulation, and exploitation.
Wartime heightens the stakes of this game by providing ample opportunities to gather
information on an enemy whose intentions may never be truly clear, and calling for a
comprehensive defense of territory under friendly control. Failure on either account may result in
strategic losses by one side or another with a significant loss of life as the prevailing
consequence. The ultimate promise of strategic and/or tactical advantage over the enemy
therefore lies in identifying and utilizing individuals prone to swear allegiance to one side, only
to betray his or her loyalties on behalf of the other side. The manner in which this is
accomplished, the difficulties in achieving success, and the pitfalls encountered in the process
(either potential or realized) are the subjects of The Double Cross System in the War of 1939 to
1945.
Great Britain first demonstrated its prowess for espionage during World War I. So
successful was British intelligence during the war that they managed to penetrate the inner circle
of the U.S. President. The strengths of its intelligence service during this time relative to other
nations clearly evinces a nation with advanced means for gathering information. The foreword to
The Double Cross System notes: “The British were masters and whatever Americans did
similarly in the European and Mediterranean theaters stemmed from British direction and
example.” (p. ix). These means were imperfect however, and as the world braced for additional
conflict with Nazi Germany, the British started exploring the use of double-agents. The Directors
of Intelligence recognized their importance as early as July 1939. (Double Cross, p. 36).
J.C. Masterman’s book on the subject introduces the reader to the double-cross system by
aptly laying out the context for its rise in importance, then discussing the success and failures of
individual agents in Britain’s employ. The earliest of these agents, codenamed “Snow” serves as

2. a conduit for identifying the many themes and issues that resurfaced throughout Britain’s
experience using double-agents in World War II.
Snow was an emigrant to Canada who returned to England just before the outbreak war
and was employed at a firm with numerous contracts with the British admiralty. This meant that
he often travelled to and from Germany for business, thereby allowing him to routinely return
with some technical information for British consumption. (Double Cross, p. 36-37). He
managed to gain the favor of German intelligence handlers during the course of his work for
Great Britain, and accepted an espionage role for the purpose of relaying information to Great
Britain (so he claimed). (p. 37). The importance of Snow’s account is to demonstrate early on
the uncertainty regarding agent loyalties, and the methods in which agents communicated with
one side or the other. Snow briefly disappeared in 1939 after he left on a trip to Germany, and
was consequently detained by the British when he resurfaced a few months later and tried to
arrange a meeting with his handlers. Masterman notes that it was precisely while Snow was in
prison that “the double-cross system was well and truly launched.” (p. 40).
Using a secret wireless transmitter from Germany installed in his cell, he communicated
with the German Abwehr (military intelligence) about plans to carry out sabotage in South
Wales. “Very soon he was receiving a variety of orders and requests for information.” (p. 40).
He was subsequently dispatched on a mission to meet German handlers in the North Sea,
accompanied by an MI-5 informant. The details are not especially important except to note that
during the course of the operation, both began to suspect the other of actually working on behalf
of Germany, resulting in Snow’s detainment (again) and worse, the operation’s near complete
failure. (p. 45). Thus, in the first chapter of Masterman’s book, the reader is presented with the
challenge at the heart of the double-cross system: how to ensure continuing loyalty of an agent in
circumstances where he or she is frequently communicating with the enemy; and the question of
what was gained from this experience.
The British successes from involvement with Snow alone consisted of:
● The discovery of “not less than three German agents” inside the U.K.
● Knowledge of Abwehr (German military intelligence) personalities and methods
● Knowledge of German wireless codes and cyper procedure
Double Cross, p. 41

3. In the ensuing pages, Masterman expounds upon several of these ideas and adds a few
more by relating accounts of other double-cross agents, and commenting on the lessons learned
from each experience. The result is a deftly-woven narrative that depicts the evolution of
Britain’s double-cross system. Discussing operational security surrounding the possible use of
[German] parachutists as double-agents for instance, he notes that their capture had to be
“unobserved except by a very few, and those trustworthy, people--otherwise a statement in the
press or injudicious talk would sooner or later enable the Germans to deduce that the particular
spy had in fact been caught.” (p. 49) Capture of a double-agent represented one of the greatest
fears held by the British while managing the double-cross system because of the repercussions
that would result to the system as a whole. Masterman notes: “If the Germans, so we thought,
once gained full knowledge of our procedure in one important double-cross case, they would
inevitably become suspicious of the rest, examine them in every detail, and end by guessing at
the truth about them all.” (p. 128). The notion that agent capture would result in catastrophe to
the British is especially important considering the persistent belief throughout the war that
double-agents were destined to participate in some singular, grand deception. This deception
later materialized in the form of the D-Day invasion into France.
The allied invasion into France on D-Day was arguably the single greatest deception of
World War II. Masterman humbly argues that “agents were only one of the channels through
which deception was carried out” but the effects their actions had on the Germans, as he recounts
in his chapter on the subject, cannot be understated. (p. 162). “The essence of counterespionage
is prevention,” he writes, and “very often we have to remind ourselves that the most real
successes of M.I.5 are represented by the fact that certain things never happened at all.” (p. 87).
Consequently, one of the uses to which double-agents may be most effectively tasked is the
transmission of information that persuades an adversary not to take certain action.
Leading up to the D-Day invasion for instance, the Germans had long suspected invasion
at a number of locations as diverse as Norway and Northern Africa. The options narrowed
however, as time progressed and Nazi-controlled territory shrinked in size. Thus, when the date
for D-Day approached, double-agents needed to persuade Nazi high command more than simply
that an invasion would not occur on the coast of France. Instead, double-agents needed to lay the
groundwork to persuade the Germans that the coming D-Day invasion (about which the Germans
did not know until after its launch) was merely the first of two invasions, with follow-on attacks

4. coming through the Pas de Calais. (p. 156). They accomplished this primarily by transmitting
information about notional forces separate from the actual invading forces that were busy
training in Scotland, and east and southeast England. Though a simple task of transmitting
information by wireless sets, the evidence of the success of this deception later became apparent
when allied forces captured German documents in Italy, which illustrated the divisional signs of
these notional forces. (p. 156). More importantly, this deception carried dividends on the day of
the invasion and thereafter by virtue of how the German high command actually reacted.
Multiple Panzer divisions and numerous infantry divisions, all stationed in France, converged on
the Pas de Calais in anticipation of an attack that never came. (p. 158). What role these forces
may have played in repelling the D-Day invasion is lost to speculation but the impact was
nevertheless clear:
“In all some seven offensive German divisions...were retained in the Pas de Calais area
for a
fortnight after D Day. It was the opinion of [German General] Jodl, if any credence is to
be given to newspaper reports, that fifteen divisions had been held in the Pas de Calais
area to counter any landing there and to protect V weapon sites, and that this had been a
fatal strategic error of the German command.”
(p. 158).
There are at least two important notes to this deception:
First, the Germans reacted to the false information transmitted by the double-agents
working for the British. Throughout the book, Masterman explains that double-agents are useful
because they not only gather information that can be used offensively, as when they are able to
discover an adversary’s strategic or tactical plans, but also provide misinformation that can be
used defensively, to divert an adversary away from friendly forces. D-Day represents the latter
situation because the Germans, by this point, were already in a defensive mode and providing
them with false information regarding the true nature and location of the allied invasion helped
to ensure operational security for landing forces.
Second, the deception was organized in such a way that when D-Day occurred, the
Germans not only did not discredit the double-agents working for the British but in fact believed

5. wholeheartedly in the falsities the agents continued to transmit. Masterman describes this point
well:
“Each successive step served to confirm the truth of the whole cover plan. Thus when the
troops of the real formations reached France, they were always the troops who had been
identified and reported upon by the agents. In consequence the Germans, finding these
reports which they could check from prisoners accurate, were disposed to believe with
equal confidence in the rest of the reports which concerned the troops, real and notional,
still in England.”
(P. 158)
The overwhelming success of the D-Day invasion was therefore not only a strategic success for
allied forces but evidently an enormous success in deception and validation of the double-cross
system.
Masterman’s book ultimately recounts a narrative of the double-cross system in which
German intelligence apparently never had a chance. This runs counter to the conclusion
presented by Masterman himself who insists “What evidence there is goes to show that Germans
were at least our equals in all the arts connected with espionage and coutnerespionage.” (p. 187).
This begs the question therefore--what explains the successes of the British double-cross system
and the Germans’ failure to effectively detect and dismantle it?
An intelligence service free from personal considerations is one, according to Masterman;
the very nature of the game itself is the other. These explanations deserve greater attention than
can be provided here and are insufficient for the scope of courageous work provided by British
double-agents, but perhaps the question is more important than the answers. If The Double Cross
teaches the reader anything, it is that operating in the field of intelligence necessarily requires
navigating uncertainty. Loyalty for some is often fluid and it is when that fluidity is most
effectively exploited that the greatest successes are brought to bare.