period Panzer I, Panzer II, Panzer III and the most advanced Panzer IV. In accordance with the ideas of Heinz Guderian, German tanks and mechanized support units (motorized artillery, etc.) were used in massive, mechanized spearhead (Schwerpunkt) attacks, serving as highly mobile units to punch holes in the enemy line and isolate selected enemy units, which the infantry would then encircle and destroy while the armored and mechanized forces pushed forward to repeat the process, eventually breaking through enemy frontlines and then dispersing, causing confusion in the rear areas and severing lines of supply and communication. Less mobile mechanized infantry and regular infantry (who, along with their horse-drawn artillery support, vastly outnumbered their mechanized comrades) would then in theory follow-up the panzer divisions' penetration into enemy territory. The Heer was closely supported by the Luftwaffe, especially by dive bombers that attacked and disrupted the enemy's supply and communications lines and spread panic and confusion in its rear, thus further paralyzing the enemy's defensive capabilities. Mechanization was the key to this German tactic first revealed in the September Campaign and nicknamed blitzkrieg (lightning war) by contemporary journalists, who found the name fitting because of the unprecedented speed and mobility that were its underlying characteristics. Despite the term blitzkrieg being coined by the Allies during the Polish September Campaign of 1939, historians (such as Matthew Cooper) generally hold that German operations in Poland were more traditional than revolutionary. Cooper, for one, writes (in The German Army (1976)) that Heer strategy was more inline with Vernichtungsgedanken, or a focus on envelopment to create pockets in broad-front annihilation. Mechanized forces were deployed among the three German concentrations without strong emphasis on independent use, being used to create or destroy close pockets of Polish forces and seize operational-depth terrain in support of the largely unmotorized infantry which followed. Luftwaffe Aircraft (particularly fighter and ground attack aircraft) played a major role in the fighting. Bomber aircraft purposely attacked cities and civilian targets causing huge losses amongst the civilian population in what became known as terror bombings. The Luftwaffe forces consisted of 1,180 fighter aircraft (mainly Bf 109s), 290 Ju 87 Stuka dive bombers, 290 conventional bombers (mainly of the He 111 and Do 17 types), and an assortment of 240 naval aircraft. In total, Germany had close to 3,000 aircraft (~2,000 of them can be considered militarily modern) with half of them deployed on the Polish