根据韩战期间真实战事改编。1950年6月25日，北韩挥军越过三八线突袭南韩，三日攻陷汉城（今首尔），战线不断南进。在美军及联合国军支援下，南韩军逆势反击。美军指挥官麦克亚瑟提出代号为「铁铬行动」的仁川登陆计划，该计划急需一支大队的兵力从侧翼阻击扰敌、声东击西，通过长沙里切断北韩军的补给线。
由于任务本身极其艰钜，加上南韩国军当时兵力薄弱，无法抽调足够正规军支援，军方不得不把这项任务交付给772名学生兵执行，这些学生兵平均年龄只有17岁，仅仅接受了两星期的军事训练，在毫无实战经验的情况下投身战场。行军路上固然杀机重重，战友内部也诸多衝突，年少气盛，迸发出各种角力。
仁川登陆战前夕，长沙里登陆任务如期执行，这群徒有一腔热血但战力薄弱的学生们，无可避免地接受命运中最残酷的考验：穿越炮火与海浪，浴血长滩，馀下部队身陷敌军重重围剿，直至弹尽粮绝，挣扎于阵亡与倖存的分界线上…
Based on the incredible true story of Jangsari Landing Operation. When North Korea invades South Korea on June 25, 1950, they pushed South Korea and its ally US Army to the southernmost city. U.S. General MacArthur planned Operation Chromite, which would see the joint allied forces to take back a strategic location of Inchon and in order for it to succeed, he needed a small battalion to flank the North Korean army and eliminate their supply line at Jangsari beach.
Having lost his family on his retreat away from North Korea before the War, a model student Choi Sung-pil enlists in the army to fight for the South. Ki Ha-ryun is a rebellious youth from the South who volunteers to fight in the war. All of the 772 students and youths are like them who are barely out of school with only 2 weeks of boot camp training. Task force commander Captain Lee Myung-jun knows that it’s a long shot, but he has no choice but to lead them into a crucial mission. Meanwhile, US war correspondent Maggie braves the dangers of the battlefield to report on the war in the frontlines. She feels empathy for the Korean students who must go into battle on behalf of the veteran soldiers for their country, and tries to do what she can on her end to rescue them.
With little ammo, scant food supplies and raggedy weapons, can the students successfully carry out their mission and return home safely?