The Karbala 4 operation plan under the title "Special Tactics" was designed by the most elite war commanders after about a thousand hours of work on the maps.This operation started on December 24, 1986, in the axis of Khorramshahr to Mino Island to capture Umm Rasas and Abul Khasib Island and close the road from Basra to Faw, but due to the vigilance of the enemy and the failure to fulfill the principle of tactical and time surprise, it was not defeated. This article tries to answer these questions: Why did the Karbala 4 operation take place? Secondly: What were the reasons for its failure? Thirdly: What effects and results followed? The research method is descriptive-analytical. The findings showed that Iran started this operation to determine the fate of the war and achieve a just peace. Although it could not reach the predetermined goals and the operation was stopped after 8.5 hours. but the effects of that operation were so great that Karbala 4 cannot be counted among absolute failures; because the first essential factor in the complete ignorance of the enemy from carrying out new operations by internal forces and the lack of luck in adopting an efficient defense strategy in Shalamche region; to such an extent that by releasing many forces and leaving the battle area by the commanders, it practically caused the enemy to be completely surprised in the Karbala 5 operation.