The Ju 87s reverted to ground attack missions for the campaign after the opening air attacks. Ju 87s were involved in the controversial but effective attacks at Wieluń. The lack of anti-aircraft artillery in the Polish Army magnified the impact of the Ju 87. At Piotrków Trybunalski I./StG 76 and I./StG 2 destroyed a Polish infantry division de-training there. Troop trains were also easy targets. StG 77 destroyed one such target at Radomsko. During the Battle of Radom six Polish divisions trapped by encircling German forces were forced to surrender after a relentless four-day bombardment by StG 51, 76 and 77. Employed in this assault were fragmentation bombs, which caused appalling casualties to the Polish ground troops. Demoralised, the Poles surrendered. The Stukas also participated in the Battle of Bzura which resulted in the breaking of Polish resistance. The dive bomber wings ("Sturzkampfgeschwader") alone dropped 388 tonnes (428 tons) of bombs during this battle. During the Siege of Warsaw and the Battle of Modlin, the Ju 87 wings contributed to the defeat of well-entrenched and resolute Polish forces. IV(Stuka)./LG 1 was particularly effective in destroying the fortified Modlin.