 South Vietnamese forces had already crossed the border on 30 April , launching Operation Toan Thang 42 . 12 ARVN battalions of approximately 8 @,@ 700 troops ( two armored cavalry squadrons from III Corps and two from the 25th Division and 5th Infantry Divisions , an infantry regiment from the 25th Infantry Division , and three Ranger battalions and an attached ARVN Armored Cavalry Regt from the 3rd Ranger Group ) crossed into the Parrot 's Beak region of Svay Rieng Province . The offensive was under the command of Lieutenant General Đỗ Cao Trí , the commander of III Corps , who had a reputation as one of the most aggressive and competent ARVN generals . During their first two days in Cambodia , ARVN units had several sharp encounters with PAVN forces . The North Vietnamese , forewarned by previous ARVN incursions , however , conducted only delaying actions in order to allow the bulk of their forces to escape to the west . 
 South Vietnamese forces <a href='been_done' title='1'><mark>had</mark></a> already crossed the border on 30 April , launching Operation Toan Thang 42 . 12 ARVN battalions of approximately 8 @,@ 700 troops ( two armored cavalry squadrons from III Corps and two from the 25th Division and 5th Infantry Divisions , an infantry regiment from the 25th Infantry Division , and three Ranger battalions and an attached ARVN Armored Cavalry Regt from the 3rd Ranger Group ) crossed into the Parrot <a href='null_genetive' title='2'><mark>'s</mark></a>Beak region of Svay Rieng Province . The offensive was under the command of Lieutenant General Đỗ Cao Trí , the commander of III Corps , <a href='null_relcl' title='3'><mark>who</mark></a>had a reputation as one of the most aggressive and competent ARVN generals . During their first two days in Cambodia , ARVN units had several sharp encounters with PAVN forces . The North Vietnamese , forewarned by previous ARVN incursions , however , conducted only delaying actions in order to allow the bulk of their forces to escape to the west . 
South Vietnamese forces done already crossed the border on 30 April , launching Operation Toan Thang 42 . 12 ARVN battalions of approximately 8 @,@ 700 troops ( two armored cavalry squadrons from III Corps and two from da 25th Division and 5th Infantry Divisions , an infantry regiment from tda25th Infantry Division , and three Ranger battalions and an attached ARVN Armored Cavalry Regt from the 3rd Ranger Group ) crossed into thdaarrot  Beak region of Svay Rieng Province . The offensive was under thedammand of Lieutenant General Đỗ Cao Trí , the damander of III Corps , had a reputation as one of the mda aggressive and competent ARVN generals . durin their first 2 days in Cambodia , ARVN units had several sharp encounters with PAVN forces . The North Vietnamese , forewarned by previous ARVN incursions , however , conducted only delaying actions in order to allow the budaof their forces to escape to the west .