Kaiser Karl VI represented a significant improvement over the preceding design—Kaiserin und Königin Maria Theresia—being faster and more heavily armed and armored.

Kaiser Karl VI spent the first decade in service rotating between the training and reserve squadrons, alternating with Sankt Georg.

In 1910, Kaiser Karl VI went on a major overseas cruise to South America, visiting Brazil, Uruguay, and Argentina; this was the last trans-Atlantic voyage of an Austro-Hungarian warship.

The fleet had until then been centered on large ironclad warships, but had been unable to continue building vessels of that type under the direction of the previous Marinekommandant, Vizeadmiral Friedrich von Pöck, owing to the refusal of the Imperial Council of Austria and the Diet of Hungary to grant sufficient naval budgets.

Sterneck decided to adopt the concepts espoused by the French Jeune École (Young School), which suggested that flotillas of cheap torpedo boats could effectively defend a coastline against a fleet of expensive battleships.

Lollok's proposal was also 6,000 tons, and instead of carrying all eight 15 cm guns in main-deck casemates, four would be moved up to open mounts on the upper deck.

[4] The naval command selected Kellner's second design, although it mandated a change to water-tube boilers for increased engine power, which in turn necessitated the addition of a third funnel.

The new cruiser, named Kaiser Karl VI, was about 1,000 long tons (1,000 t) larger than her predecessor, Kaiserin und Königin Maria Theresia, and was a significantly more effective vessel as a result, being a knot faster, mounting more powerful guns, and carrying heavier armor.

[12] In mid-1910, Kaiser Karl VI conducted the last trans-Atlantic cruise of an Austrian vessel, when she visited Brazil, Uruguay and Argentina.

Their decoy mission complete, Kaiser Karl VI and the rest of the fleet returned to port without engaging any British forces.

At the time, Kaiser Karl VI was the only large warship in the harbor, and she assisted the local army artillery in attempting to suppress the hostile guns.

[15] By the end of August, the mobilization of the fleet was complete; Kaiser Karl VI was assigned to the Cruiser Flotilla, which was commanded by Vice Admiral Paul Fiedler.

[18] By early 1918, the long periods of inactivity had begun to wear on the crews of several warships at Cattaro, including Kaiser Karl VI.

On 1 February, the Cattaro Mutiny broke out, starting aboard Sankt Georg and quickly spreading to Kaiser Karl VI.

[19] Officers were confined to their quarters while a committee of sailors met to formulate a list of demands, which ranged from longer periods of leave and better rations to an end to the war, based on the United States President Woodrow Wilson's Fourteen Points.

The following day, shore batteries loyal to the government fired on the old ironclad Kronprinz Erzherzog Rudolf, which prompted many of the mutinous ships to abandon the effort.

Late in the day on 2 February, the red flags were struck from Kaiser Karl VI and she rejoined the loyalist ships in the harbor.