The 2nd Battalion, faced only light resistance, while the 9th Battalion , ran into the  soldiers of the enemy 12th SS Panzer Division, who had allowed the barrage to pass over their positions before opening fire.

1 从语法上讲，who引导的定语从句应该修饰离它最近的名词，而不是越过最近的名词去修饰一个更远的名词。没有道理。

2 从逻辑上讲，二营和九营都是进攻方，从句谓语had allowed the barrage to pass over their positions显然是防守方的行为。因此，who的先行词应为the soldiers of the enemy 12th SS Panzer Division.

3 句首主句的主语和谓语之间也用了逗号。while从句主语谓语之间的逗号呼应主句的逗号，与定语从句无关。这种逗号的用法可能是为了将主句和从句进行对比。

译文：

二营只遇到了轻微的抵抗，但九营却与盖世太保第十二装甲师的士兵遭遇，后者先让掩护炮火越过他们的位置，然后才开火。