In the newspaper “Neuigkeits-Welt-Blatt. J. F. S. Hummel. 1876. Kirsch” from the Austrian National Library we can read of the Serbian attack on the Austrian Maros ship in 1876.
Cited:
“The Serbian Attack on the Austrian Monitor Maros: Even the Serbian government calls the shelling of the Austrian monitor, the turret-armored ship Maros, on the 19th of this month from the Belgrade fortress, an extremely reprehensible incident, which we already discussed yesterday and will describe in detail elsewhere today.
Just two days before this event, the Austrian Consul General, Prince Wrede, had received the satisfaction he demanded for the police arrest and search of the steamer Radetzky, and the two Danube monitors sent to Belgrade to emphatically support this demand for redress were therefore to be recalled.
Prince Wrede, along with Count Bray, Lieutenant Colonel Raab, and Consular Trainee Count Vass, were on board the Maros to observe the ship’s maneuvers. All four gentlemen were in the turret when shots rang out; one cannonball lodged in the mast. The monitor returned this completely unexpected attack with a cannon shot, whereupon another shot was fired at the ship.
The monitor then moved in front of the sentry post, but the man who had fired the shots at the monitor from the lower fortress withdrew. Fortunately, the two shots did not hit anyone. However, 14 men were wounded by the explosion of a grenade while a cannon was being loaded inside the ship’s conning tower; 3 of them have already died. Consul General Prince Wrede immediately returned to Belgrade to lodge complaints.
Soon after, Minister President Ristics appeared before Prince Wrede and informed him that the government had abdicated to give Prince Milan a freer hand. Ristics offered every kind of apology. He reported that the fortress command had been ordered not to fire, even if the monitor were to fire shots at the fortress, as Prince Wrede had immediately ordered in the event of a repeat of the assassination attempt.
Later, Adjutant General Protics came to Wrede to reiterate the Prince’s regret and apology. A similar assurance was also given. The Serbian Foreign Ministry there was summoned. He was telegraphed by Prince Milan to Belgrade to form a new ministry. Before his departure, Dr. Zukics had a meeting with Minister Count Andrássy.
Lesterer explained that the imperial government felt compelled to demand a visible commitment to its interests on the border in order to put an end to Serbian excesses, since Serbia’s unpredictable behavior, based on previous experience, defied all calculation. An occupation of Serbia by Austrian troops is, it is said, being seriously discussed in political circles.”

Source
Neuigkeits-Welt-Blatt. J. F. S. Hummel. 1876. Kirsch”. Austrian National Library.
