SMS Don Juan d'Austria[a] was the third member of the Kaiser Max class built for the Austrian Navy in the 1860s.

She carried her main battery—composed of sixteen 48-pounder guns and fifteen 24-pounders—in a traditional broadside arrangement, protected by an armored belt that was 110 mm (4.3 in) thick.

There she was heavily engaged in the center of the melee; she traded broadsides with the Italian ironclad Re di Portogallo and was hit three times by the turret ship Affondatore, though she received little damage.

After the war, Don Juan d'Austria was modernized slightly in 1867 to correct her poor seakeeping and improve her armament, but she was nevertheless rapidly outpaced by naval developments in the 1860s and 1870s.

The sides of ship's hull were sheathed with wrought iron armor that was 110 mm (4 in) thick and extended from bow to stern.

Don Juan d'Austria was sent with the wooden ship of the line Kaiser, the screw corvette Erzherzog Friedrich, and the paddle steamer Elisabeth under Vice Admiral Bernhard von Wüllerstorf-Urbair to reinforce a smaller force consisting of the screw frigates Schwarzenberg and Radetzky under then-Captain Wilhelm von Tegetthoff.

Tegetthoff received a series of telegrams between 17 and 19 July notifying him of the Italian attack, which he initially believed to be a feint to draw the Austrian fleet away from its main bases at Pola and Venice.

Don Juan d'Austria initially attempted to follow Tegetthoff's flagship, Erzherzog Ferdinand Max, but quickly lost contact with her in the ensuing melee.

Don Juan d'Austria became surrounded by Italian vessels, prompting her sister Kaiser Max to come to her aid.

Don Juan d'Austria thereafter engaged Re di Portogallo for around half an hour before shifting targets back to Affondatore.

[10] By this time, Re d'Italia had been rammed and sunk and the coastal defense ship Palestro was burning badly, soon to be destroyed by a magazine explosion.

The Italian ships never came, and on 12 August, the two countries signed the Armistice of Cormons; this ended the fighting and led to the Treaty of Vienna.

[12] The fleet embarked on a modest modernization program after the war, primarily focused on re-arming the ironclads with new rifled guns.

Reconstruction projects were routinely approved by the parliament, so the navy officially "rebuilt" Don Juan d'Austria and her sister ships.