capital. chaima spent months with them. speaking from syria, he explained why the battle for raqqah was different. mostly there was like really heavy clashes going on, like street by street, corner by corner. but here, no. reporter: he said the biggest challenge was the extraordinary number of improvised explosive devices left behind by isis before they retreated. the traps were usually set on lower floors. so the fighters learned to enter buildings higher up by blasting holes in external walls. and crawling perilously across narrow makeshift bridges. the other challenges he said, was snipers firing from tall buildings. those guys they know how to fight very well. they know how to shoot very well. reporter: chaim said the best answer to sniper fire was air