On the early morning of 15 May 1917, the Austro-Hungarians made their most serious attack of the war on the naval drifters controlling the barrage. "Bristol" was the "ready ship" at Brindisi and was at a half-hour's notice for sea; she departed at 04:50, escorted by two Italian destroyers, in an attempt to intercept the three Austrian light cruisers that had conducted the attack. Contrammiraglio (Rear-Admiral) Alfredo Acton, commander of the ships at Brindisi, ordered that her speed be limited to to prevent her from getting too far ahead of the other ships now raising steam. One of these was "Bristol"s half-sister , which departed at 05:36, also escorted by a pair of Italian destroyers. The "Dartmouth" group overtook "Bristol" and her consorts by 07:12 and were joined by the Italian scout cruiser around 07:40. Acton deployed his cruisers in line abreast with "Aquila" leading them and the destroyers guarding the flanks. "Bristol"s bottom was foul, however, and limited the group to a speed of .