(KABUL) — The Afghan army is waging its largest-ever solo offensive against the Taliban, hoping to strike a decisive blow ahead of the spring fighting season and prove it can rout the insurgents without the aid of U.S. and NATO combat troops. Afghan troops have been slowly pushing up through a fertile river valley in the southern Helmand province, with special forces mounting nighttime helicopter raids into mud brick compounds and ground troops gradually advancing across the poppy fields that in past years have furnished the insurgents’ main cash crop. U.S.