On the morning of 9 May, the two squadrons encountered each other off the island of Heligoland, then controlled by neutral Great Britain. Tegetthoff attacked with his two frigates while the slower Prussian vessels lagged behind, unable to effectively engage the Danish warships. Tegetthoff's flagship, "Schwarzenberg", bore the brunt of the Danish gunfire and caught fire three times, the last of which could not be put out quickly and forced Tegetthoff to seek shelter in the neutral waters around Heligoland. Though Denmark claimed a tactical victory in the battle, the Danes were forced to end the blockade of the German coast. An armistice came into effect three days after the Battle of Heligoland. By the time fighting broke out again in June, further Austrian warships had arrived to strengthen the Austro-Prussian naval forces, and the Danes did not seek to challenge them.