Soon afterward, as part of what became known as the "Tanker War", the Federal government of the United States reflagged and renamed 11 Kuwaiti oil tankers. In Operation Earnest Will, these tankers were escorted by USCENTCOM's Middle East Force through the Persian Gulf to Kuwait and back through the Strait of Hormuz. By late 1988, the regional strategy still largely focused on the potential threat of a massive Soviet invasion of Iran. Exercise Internal Look has been one of CENTCOM's primary planning events. It had frequently been used to train CENTCOM to be ready to defend the Zagros Mountains from a Soviet attack and was held annually. In autumn 1989, the main CENTCOM contingency plan, OPLAN 1002-88, assumed a Soviet attack through Iran to the Persian Gulf. The plan called for five-and-two-thirds US divisions to deploy, mostly light and heavy forces at something less than full strength (apportioned to it by the Joint Strategic Capability Plan [JSCAP]). The original plan called for these five-and-two-thirds divisions to march from the Persian Gulf to the Zagros Mountains and prevent the Soviet Ground Forces (army) from seizing the Iranian oil fields. After 1990, General Norman Schwarzkopf reoriented CENTCOM's planning to fend off a threat from Iraq, and Internal Look moved to a biennial schedule. There was a notable similarity between the 1990 Internal Look exercise scripts and the real-world movement of Iraqi forces which culminated in Iraq's invasion of Kuwait during the final days of the exercise. U.S. President George Bush responded quickly. A timely deployment of forces and the formation of a coalition deterred Iraq from invading Saudi Arabia, and the command began to focus on the liberation of Kuwait. The buildup of forces continued, reinforced by United Nations Security Council Resolution 678, which called for Iraqi forces to leave Kuwait. On 17 January 1991, U.S. and coalition forces launched Operation Desert Storm with a massive air interdiction campaign, which prepared the theater for a coalition ground assault. The primary coalition objective, the liberation of Kuwait, was achieved on 27 February, and the next morning a ceasefire was declared, just one hundred hours after the commencement of the ground campaign. The end of formal hostilities did not bring the end of difficulties with Iraq. Operation Provide Comfort, implemented to provide humanitarian assistance to the Kurds and enforce a "no-fly" zone in Iraq, north of the 36th parallel, began in April 1991.