Bert Sas Bert Sas ( 1 August 1892 – 20 October 1948 ) was the Netherlands military attaché in Berlin at the time of the German invasion of the Netherlands in May 1940 . Gijsbertus Jacobus ( Bert ) Sas was born in Leeuwarden . He was named after his father , a soldier who by his pension had reached the rank of Lieutenant Colonel . His mother Geertrui Huiber was 20 years younger than her husband . Bert was the youngest of 3 children , and attended a secondary school in Leeuwarden . In 1910 he went to the " Koninklijke Militaire Academie " in Breda . During World War I , in 1917 , he was promoted to First Lieutenant and married Maria Johanna van der Minne . From 1923 until 1926 he followed the training for staff officier at the " Hogere Krijgsschool " . After this he obtained another staff function in The Hague . In 1928 he was promoted to the rank of Captain and became head of the most important bureau of the 2nd division where all of the important military questions were handled . However during the period from 1928 until 1936 , military expenditure was strictly limited . Between 1936 and 1937 he was the military attaché in Berlin for 10 days per month , spending the remaining 20 days in The Hague . He was then recalled to The Hague , where he functioned as the right hand of general Reynders in the role of head of the operations division . In March 1939 , following the German annexation of the Sudetenland , Reynders sent him back to Berlin . This time he set up residence there with his wife Miep . In Berlin he immediately restored his friendship with the German colonel Hans Oster . Oster had obtained an important position as the right hand of Wilhelm Canaris at the German Abwehr , the espionage and counter - espionage service of the army . They were connected not only through their mutual dislike for the Nazi regime . Their friendship dated from the beginning of the 1930s , when they first met , possibly when Sas was working in The Hague . Oster passed him all important information that he obtained . He did not do this out of sympathy for Sas , but because he considered it his duty to Germany . He did not see himself as a traitor , but someone who did his duty to the decent Germany that he loved . At end of August 1939 he warned The Hague that a war with Poland was about to begin . He gave 25 August 1939 as the invasion date , but this date passed by . At 14 : 50 on that day Hitler gave the order for the invasion , but revoked it when he heard that England was not going to concede . Sas ' credibility suffered . When he reported on 31 August that the war was now close , the head of intelligence , Van der Plassche did not believe him . Sas was the only one who delivered this report : London and Paris gave reassurance . However the Netherlands mobilised at the insistence of Queen Wilhelmina . General Reijnders , his superior in The Hague , was positive over Sas ' information . The relationship with general Reijnders remained good as long as the Netherlands neutrality was not discussed . During September and October , Sas obtained more signals that the neutrality of the Netherlands would not remain inviolate . However Oster assured him that only Belgium would be the target . However Sas did not believe this . At his insistence , Oster obtained further information from the Germain headquarters in Zossen . This showed that Sas was correct : the Netherlands would be invaded together with Belgium , and that the violation of neutrality would not be limited to a passage through southern Limburg . Sas died in the 1948 KLM Constellation air disaster in Scotland .