For the next eight months, both sides were on a defensive footing (with the exception of the Battle of Dezful), as the Iranians needed more time to reorganise their forces after the damage inflicted by the purge of 1979–80. During this period, fighting consisted mainly of artillery duels and raids. Iraq had mobilised 21 divisions for the invasion, while Iran countered with only 13 regular army divisions and one brigade. Of the regular divisions, only seven were deployed to the border. The war bogged down into World War I-style trench warfare with tanks and modern late-20th century weapons. Due to the power of anti-tank weapons such as the RPG-7, armored manoeuvre by the Iraqis was very costly, and they consequently entrenched their tanks into static positions.