B17s were in combat in the Pacific from the first day of the war, with mixed results. A flight landing in Hawaii from the mainland was attacked diring the Japanese raid on Pearl Harbor. Others were destroyed on the ground in the Philippines, but a few remained operational there and carried out missions. Some evacuated to Australia, where additional units were sent.
There were also B17s at the Battle of Midway
They saw additional use as long range patrol aircraft, and later as air sea rescue, with a lifeboat in the bomb bay.
The B17 saw much less use in the Pacific after 1943.
There were attempts to use B17s with conventional gravity bombs to sink warships. From higher altitudes,this was not very effective.