袭击 (xí jī) means 'to attack' with a strong emphasis on surprise, stealth, or a raid — it is a sudden, unexpected assault (military, criminal, or even by animals). 突击 (tū jī) also means 'surprise attack' but focuses on a swift, concentrated military strike; 攻击 (gōng jī) is a broader, more general attack that can be physical or verbal and does not imply surprise.