War with Spain erupted late in April 1898, and Bernadou was soon patrolling the northern coast of Cuba in Winslow. On May 8, Barnadou blockaded the port of Cardenas with USS "Machias". That day, "Machias" left for a patrol leaving only the "Winslow" for blockading. Three Spanish gunboats which were trapped in the port decided to sortie and attempt to lift the blockade, in the ensuing battle, "Winslow" damaged all three Spanish vessels and sent them back into port. On May 11, he took "Winslow" to take on coal from one of the larger warships there. Upon reporting to the commanding officer of (Gunboat No. 8), he received orders to take Winslow into the bay at Cardenas and scout for mines. "Winslow" and the revenue cutter "Hudson" searched the harbor entrance but found no mines. They rejoined "Wilmington" about noon to make their report. "Wilmington's" commanding officer decided to take the three warships into the bay in search of the three Spanish gunboats reported there. Bernadou's command marked shoal water to Wilmington's portside during the entry. Upon reaching a point about 3,000 yards from the city, a lookout spied a small, gray steamer moored alongside the wharf. Bernadou then received orders to move his ship in closer to determine whether or not the ship was an enemy warship.