On 25 December 1986, Iran launched Operation Karbala-4 ("Karbala" referring to Hussein ibn Ali's Battle of Karbala). According to Iraqi General Ra'ad al-Hamdani, this was a diversionary attack. The Iranians launched an amphibious assault against the Iraqi island of Umm al-Rassas in the Shatt-Al-Arab river, parallel to Khoramshahr. They then set up a pontoon bridge and continued the attack, eventually capturing the island in a costly success but failing to advance further; the Iranians had 60,000 casualties, while the Iraqis 9,500. The Iraqi commanders exaggerated Iranian losses to Saddam, and it was assumed that the main Iranian attack on Basra had been fully defeated and that it would take the Iranians six months to recover. When the main Iranian attack, Operation Karbala 5, began, many Iraqi troops were on leave.