During the first month of the war the Royal Air Force (RAF) mostly focused its bomber attacks against anti-shipping operations on the German Bight. RAF bombers mounted a heavy attack against shipping off Wilhelmshaven on 18 December 1939 in what became known as the Battle of the Heligoland Bight. Twenty-four twin-engine Vickers Wellington from No. 9 Squadron, No. 37 Squadron and No. 149 Squadron formed up over Norfolk heading for the island of Heligoland. Two aircraft aborted the mission due to mechanical defects, but the remaining 22 pursued the attack and were spotted by a Freya radar on the East Frisian Islands.