“主力冲击”可以翻译为 "main force's assault/charge" 或 "the assault/charge by the main force"。
Main force 指主力部队或主要力量。
Assault 或 charge 都有冲击、进攻的意思，可根据具体语境选择。
例如：
The main force's assault broke through the enemy's defenses.（主力冲击突破了敌人的防线。）
The charge by the main force was a decisive moment in the battle.（主力的冲击是战斗中的决定性时刻。）