The Black Chamber in the Dutch Republic During the War of the Spanish Succession and Its Aftermath, 1707–1715

Abstract

. 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 ( -), 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 -, one related to an undercover agent of the Bavarian Elector in the Dutch Republic during the years -and one related to a French emissary to the state council in Brussels during the period -. 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.* I should like to express my gratitude to H. J. Hardy, Hans van der Meer and A. J. Veenendaal jr, who all yielded in their own way a vital contribution to the writing of this article. " Christopher Andrew, ' The nature of military intelligence ', in Keith Nelson and B. J. C. McKercher, eds., Go, spy the land : military intelligence in history (Westport, CT, and London, ), pp. - ; David Kahn, The codebreakers (New York, ), pp. -. '! Schnath, Geschichte Hannovers, , p. . '" Hanover, Niedersa$ chsisches Hauptstaatsarchiv, Cal. Br.\, fos. -, Robethon to Georg Ludwig, The Hague,  June . '# The Hague, Algemeen Rijksarchief (ARA), Legatiearchief Barbarije, inv. nr . The folder was identified in the course of a general survey of all code material in Dutch archives. '$ This attribution was first made by A. J. Veenendaal jr and subsequently corroborated by H. J. Hardy, a specialist in the field of identification of handwriting working at the Forensic Laboratory of the Justice Department. '% Robert Fruin, ed., Overblyfsels van Geheugchenis der besonderster voorvallen uit het leeven van den Heere Coenraet Droste (Leiden, ), pp. -.

Deciphering a Letter to Louis XIV from his Ambassador to the Dutch Republic, le Comte d’Avaux, 1684

“…D'Avaux recorded his own version of the events in (d'Avaux, 1754). A background on Dutch cryptography is given in (De Leeuw, 1999).…”