commando unit; guerrilla unit
Military term for a small, mobile unit that conducts raids and irregular warfare.
遊撃隊が敵の補給線を断った。
The commando unit cut the enemy's supply line.
遊撃隊 is a more formal military term for an irregular strike force, while ゲリラ is the everyday loanword for guerrilla fighters or tactics.
From 遊撃 (yūgeki, 'raid, guerrilla attack') + 隊 (tai, 'unit, corps').