This article reveals the existence of a hitherto unknown Black
Chamber in the Dutch
Republic and the identity of its principal codebreaker, Abel Tasien d'Alonne
(1646–1723), acting also
as private secretary to Grand Pensionary Heinsius. On the basis of an analysis
of a number of
previously unidentified worksheets, three cases are put together that merited
d'Alonne's attention, one
related to a French diplomat at the court of the Bavarian Elector during
the years 1707–9, one related
to an undercover agent of the Bavarian Elector in the Dutch Republic during
the years 1711–12 and
one related to a French emissary to the state council in Brussels during
the period 1714–15. The
emergence of a Black Chamber in The Hague is remarkable because the Dutch
could always call upon
the Black Chamber of Hanover for the solution of any intercepted, coded
documents. This indicates
that the development of inter-allied relations during the war played a
more important role in the rise
of the Dutch Black Chamber than one would expect.