The British response to Haselden’s telegram was carefully calibrated. London acknowledged the discovery, asked for the return of the official documents Martin had been carrying, and expressed appropriate concern about the dead officer’s possessions. This was exactly what the Germans would expect British authorities to do, and it therefore confirmed the legitimacy of the incident.
The German intelligence involvement was handled primarily through Adolf Clauss, who made contact with Spanish naval authorities in Huelva and obtained access to the documents. Exactly how he obtained this access is documented in various accounts but the details are somewhat contested. What is established is that the documents were photographed by German agents while in Spanish custody and that the photographs were sent to German intelligence headquarters.
The Spanish position throughout this process was one of deliberate ambiguity. Officially, Spanish naval authorities were treating the incident as the death of a British officer and returning his possessions to British authorities. Unofficially, or at a remove, they were allowing German intelligence access to the documents before returning them. Whether this reflected official Spanish policy or the individual initiative of officers with German connections is a question that involves the murky territory of Franco’s wartime intelligence relationships and cannot be definitively resolved from the available evidence.
The documents were returned to British authorities having been examined. The question of whether the return showed signs of tampering — whether the documents had been opened and resealed — was one the British had anticipated. Montagu’s account describes examining the returned documents for evidence of access. The wax seals on the envelope containing the documents were a key point of analysis. The seals showed signs consistent with having been opened and resealed, which confirmed, in the British assessment, that the documents had been read.