The Provence class was designed as an enlarged version of the Gloire-class ironclads with thicker armor, more powerful guns, and better seakeeping qualities.

[4] Flandre was the fastest ship of her class and reached a speed of 16.5 knots (30.6 km/h; 19.0 mph) from 3,852 PS (2,833 kW) on her sea trials.

Together with the ironclad Magenta, the ship visited Plymouth, England, on 17–19 July[3] to take part in the Exhibition of the Royal Agricultural Society.

[8] To reciprocate British hospitality, the French invited the Channel Fleet to visit Cherbourg on Emperor Napoleon III's birthday in August.

They arrived on 14 August and remained for four days, their crew's exchanging ship visits, touring the dockyard and participating in multiple banquets and balls.

The French ships, including Flandre, arrived later that month and remained until 2 September; their crews similarly occupied as the British were earlier.

The ship was assigned to Vice Admiral (vice-amiral) Édouard Bouët-Willaumez's squadron that was tasked to blockade German ports in the Heligoland Bight.

It left Cherbourg on 24 July and, failing to find any German ships, proceeded to Danish waters to await further orders.

Bouët-Williaumez was ordered on 2 August to split his forces with half, including Flandre, proceeding into the Baltic Sea to blockade the Prussian ports there under his command and the others to return to the Bight.

Bad weather and a series of storms beginning in late August prevented the squadron from bunkering and the ships were forced to return to France in early September.