On 21 July 1914, the Austro-Hungarian Minister of Foreign Affairs Leopold Count Berchtold sent a coded private telegram to the Austro-Hungarian Ambassador in Belgrade Baron Giesl. In his telegram, Berchtold (pictured) informs Giesl on how to deliver the Austro-Hungarian ultimatum to Serbia.
Count Berchtold to Baron von Giesl in Belgrade. Vienna, 21 July 1914.
According to the newspapers, Premier Pasic [the Serbian Prime Minister] has gone to East-Servia on election business and will not return to Belgrade before the end of the week.
If this news is confirmed it will be necessary that your Excellency, on Thursday morning, sends a letter to the first official of the Servian Ministry of Foreign Affairs by someone from the Chancellor’s office, stating that you are instructed to communicate important news to the Servian government on Thursday afternoon and would call at Ministry of Foreign Affairs between 15:00 and 17:00. You will write that your communication will probably make a speedy return of Herr Pasic necessary; the temporary Chief of the Ministry of Foreign Affairs had better, if he thought it necessary, communicate immediately with the Premier.
To avoid mistakes, I should like it to be understood that this letter must be regarded in the light of an act of courtesy on your part, to facilitate the early return and the information of the Premier. But the presentation of the note must under all circumstances take place on Thursday afternoon between 16:00 and 17:00, and should Herr Pasic be absent, the document must, be given either to his representative or to the official next in rank in the Servian Ministry of Foreign Affairs.
When the note has been delivered, your Excellency will inform me in the most urgent manner, by previously prepared cyphered telegrams in duplo [e.i. in two copies] from Belgrade and from Semlin by a member of the legation, whom you will send there on receipt of this telegram. I am anxious to have the news here on Thursday before 19:00 or 20:00, for publication and other measures to be taken.
Source: 1919 Austro-Hungarian Red Book, with minor edits.