By April 1945, Germany was evacuating its entire Norway garrison to reinforce its troops defending Berlin against the rapidly advancing Red Army. The German Navy commandeered every serviceable merchant ship in Norway to transport its soldiers and equipment.

On 11 April 1945, Norwegian Mosquito scouts sighted a convoy of merchant ships departing Porsgrunn loaded with German troops heading south. Wing Commander Junior Simmonds was assigned to lead a force of Mosquitos and escorting Mustangs to intercept the German ships.

At the same time a force of Luftwaffe Bf-109G14s was assigned to provide air cover to the convoy.