Kurt Aßmann

 Kurt Aßmann (13 July 1883&mdash;26 July 1962) was a German admiral who was present at Adolf Hitler’s Wolfsschanze headquarters on 20th July 1944, during the unsuccessful attempt on the German leader’s life (known as the 20 July Plot). He later provided key testimony to the Allies, which enabled them to piece together the moments leading up to the explosion.

20 July Plot
In his book The Rise and Fall of the Third Reich, William Shirer writes:

According to the account given Allied interrogators by Admiral Kurt Assmann, who was present [at the Wolfsschanze conference], [Claus von] Stauffenberg had whispered to [General] [Heinz] Brandt, “I must go and telephone. Keep an eye on my briefcase. It has secret papers in it”.