46th Division was a 'Second Line' formation of the Territorial Army (TA) formed just before the outbreak of war. Its virtually untrained infantry had briefly served in the Battle of France before being evacuated from Dunkirk. Lessons from that campaign and the early fighting in the Western Desert had been learned, and now every infantry division was to have its own air defence unit, equipped with 48 (later 54) towed Bofors 40 mm guns to protect against ground-attack aircraft such as the "Luftwaffe" 's feared "Stuka". The plan was to equip one battery in each divisional LAA regiment with self-propelled guns on truck chassis, but few of these were available until later in the war.