in the morning of May 16, Chiang Kai-shek personally issued another order once again to demand the 10 nationalist army-sized reorganized divisions reinforcing the besieged nationalist 74th Reorganized Division, but progress was extremely slow and by the fastest speed, it would still take days according to the progress already made: the advance of 8 army-sized reorganized divisions and 2 division-sized brigades that were closest to the besieged 74th Reorganized Division were all completely checked in the morning of May 16 by the communist forces deployed on their ways to blocking them. The battles at the Menglianggu region were fierce after the communist launched their general assault in the afternoon of May 15, with most positions changing hands multiple times. The communist 4th Column first took Mount 330, and then took the region in between Mount 520 and the western half of Mount 540, thus successfully cutting off the retreating route of the nationalists. Realizing the dangerous situation, the nationalists launched several counterattacks, but all were beaten back with stubborn enemy resistance. With the reinforcements from the communist 1st Column and 9th Column, the communist 4th Column further attacked and took Mount 520 by midnight, killing most of the defenders. The surviving nationalist defenders of Mount 520 fled to Mount 540, but the communists would not give them a break and continued their attack on Mount 540. A detachment of the communist 4th Column scaled the cliff of the western half of Mount 540 and outflanked the defenders and launched a surprise attack. The surprised nationalist defenders could not react in time and rapidly fled toward the eastern half of Mount 540, and the nationalist commander Zhang Lingfu was unable to stop his fleeing troops and his headquarters was dangerously exposed to the fire of the attacking enemy. Although the nationalist commander was able to make his timely retreat just in time from the eastern half of Mount 540 with rest of his staffs when he was forced to relocate his headquarters to Mount 570, but due to the heavy casualties of staff officers, the remaining headquarters was only a mere fraction of what it once was and could not function normally anymore like it used to. At dawn on May 16, the nationalists counterattacked the western half Mount 540 held by the communists in waves under fire cover, and the strength of their attack forces eventually grew to regimental size