Check the number.

谁也没想到的是，不出10年，美军在朝鲜战场上也遇到了中国人民志愿军的“地道战”——曾任冀中军区司令员并用一篇《冀中平原上的地道斗争》推动过地道战发展的杨成武，又把这一战术用到了抗美援朝战场上。志愿军在抗美援朝战争中共挖了长达1250公里的坑道和6240公里的各种堑壕、交通壕，在阵地战中歼敌53.32万人。- check this number!  Tunnel warfare can only be used in defensive and stationary battles.  Chinese army was in offensive in most of the battles in the Korean war and battles were fought in movements most of the time.  The tunnel warfare was only used in the later stage of the war and these battles were in small scales.  How can such battles cause so much damages?