In May 1968, the PAVN launched a multi-division invasion of Laos. The Pathet Lao effectively served as an auxiliary force to the PAVN. In June 1969 the PAVN/Pathet Lao launched Campaign Toan Thang, their first wet season offensive. Unable to match the heavy Soviet and Chinese weapons in addition to the numerical strength of the PAVN/Pathet Lao forces, the RLA took heavy losses. In September 1969 the RLA attacked PAVN/Pathet Lao positions on the Plain of Jars and along the Ho Chi Minh Trail, while initially successful the RLA forces were pushed back by the PAVN/Pathet Lao Campaign 139.