During the First (1994–1996) and Second Chechen Wars (1999–2009), Chechen rebels used RPGs to attack Russian tanks from basements and high rooftops. This tactic was effective because tank main guns could not be depressed or raised far enough to return fire, in addition, armor on the very top and bottom of tanks is usually the weakest. Russian forces had to rely on artillery suppression, good crew gunners and infantry screens to prevent such attacks. Tank columns were eventually protected by attached self-propelled anti-aircraft guns (ZSU-23-4 Shilka, 9K22 Tunguska) used in the ground role to suppress and destroy Chechen ambushes. Chechen fighters formed independent "cells" that worked together to destroy a specific Russian armored target. Each cell contained small arms and some form of RPG (RPG-7V or RPG-18, for example). The small arms were used to button the tank up and keep any infantry occupied, while the RPG gunner struck at the tank. While doing so, other teams would attempt to fire at the target in order to overwhelm the Russians' ability to effectively counter the attack. To further increase the chance of success, the teams took up positions at different elevations where possible. Firing from the third and higher floors allowed good shots at the weakest armor (the top). When the Russians began moving in tanks fitted with explosive reactive armor (ERA), the Chechens had to adapt their tactics, because the RPGs they had access to were unlikely to result in the destruction of the tank.