Saddam responded by launching chemical attacks against the Iranian positions along the highway and by initiating the aforementioned second "war of the cities", with an air and missile campaign against twenty to thirty Iranian population centres, including Tehran. Under General Sultan Hashim Ahmad al-Tai and General Jamal Zanoun (both considered to be among Iraq's most skilled commanders), the Iraqis launched air attacks against the Iranian positions and pinned them down. They then launched a pincer attack using mechanized infantry and heavy artillery. Chemical weapons were used, and the Iraqis also flooded Iranian trenches with specially constructed pipes delivering water from the Tigris River.