1 March 1864, after the start of the Second Schleswig War, Delphin was reactivated and stationed in Dänholm off Stralsund. There, she was assigned to the II Flotilla Division. On 14 April, after a minor action off the island of Hiddensee, in which Delphin did not take part, the Prussian gunboat flotilla was reduced to a reserve formation and took no further active part in the war. After the war in 1865, Delphin was tasked with surveying Eckernförde Bay outside Kiel in Holstein, which was now under the administration of the German Confederation. From 1 to 3 March, Delphin served as an ice breaker in Eckernförde Bay. In February, the naval high command had decided to send Delphin to Constantinople, the capital of the Ottoman Empire, to serve as a station ship to protect German interests in the region. Accordingly, Delphin underwent a major overhaul to prepare her for the overseas deployment. During the overhaul, her schooner rig was reduced slightly to a barquentine rig, and the boat's 24-pounder was replaced with a rifled 68-pounder gun. Delphin conducted a training cruise with the corvette to Sonderburg, Travemünde, and Wismar from 20 to 23 July. On 3 August, Delphin towed the frigate back to port after the latter had had her rigging damaged in a storm. Three days later, Delphin left Prussia for the Mediterranean Sea in company with Nymphe, stopping initially in Piraeus on 22 September. The vessels' deployment was short-lived, however, as war with Austria threatened in April 1866, and both ships were recalled to Prussia. They arrived on 3 July, the day the Prussian army decisively defeated Austria at the Battle of Königgrätz. For the remainder of the war, Delphin was assigned to the North Sea Flotilla, which was commanded by then-Korvettenkapitän (KK—Corvette Captain) Reinhold von Werner from his flagship, the ironclad turret ship . For the duration of the conflict, the flotilla operated out of Geestemünde. Without a naval threat from Austria, the Prussian navy therefore concentrated its effort against the Kingdom of Hanover. On 22 August, Delphin was decommissioned in Danzig. 1867–1881 In 1867, the high command decided to send Delphin back to the Mediterranean. She was sent to the Königliche Werft in Danzig for a reconstruction that would make the vessel more suitable for an extended overseas assignment. This included replacing old or damaged hull timbers, installing a new deck, and rebuilding the crew spaces