In the spring and summer of 1951 the war in Korea took a different form, moving from the period of sweeping offensives and withdrawals to a bitter, slow, costly, and violent operational tempo. The fighting northeast of the Hwachon Reservoir-- known as the "Punchbowl"-was some of the fiercest the Marine Corps faced in its history. Not only did the Marine Corps have to fight North Korean and Chinese armies, it also had to overcome strained inter-Service relationships that affected everything from supply to close air support (CAS). The Battle of the Punchbowl, was one of the last battles of the movement phase of the Korean War. Following the breakdown of armistice negotiations in August 1951, the United Nations Command decided to launch a limited offensive in the late summer/early autumn to shorten and straighten sections of their lines, acquire better defensive terrain, and deny the enemy key vantage points from which they could observe and target UN positions. The Battle of Bloody Ridge took place west of the Punchbowl from August-September 1951 and this was followed by the Battle of Heartbreak Ridge northwest of the Punchbowl from September-October 1951. At the end of the UN offensive in October 1951, UN Forces controlled the line of hills north of the Punchbowl.