Operation Dawn 3 or Operation Valfajr-3 was Iran's worst defeat out of all the Dawn operations. 180,000 Iranian troops participated in this attack but withering Iraqi firepower in support of deeply entrenched troops slaughtered the advancing Iranians.

The Iraqis struck back by emerging from their trenches to counter attack into Iran

Iran

Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

 and capture Mehran

Mehran, Ilam Province

Mehran , also Romanized as Mansūrābād) is a city in and the capital of Mehran County, Ilam Province, Iran. At the 2006 census, its population was 13,118, in 2,958 families.Mehran is located near the Iran's western border with Iraq...

. Although Iranian troops were highly motivated, they were poorly trained and equipped for this battle. For Iran the operation was a disaster.