Submarines are highly efficient War machine. It is easy to attack the enemies and can hide easily.
Step-by-step explanation:
20 to 30 sailors on submarines can cause more damage than 1000 soldiers on the battlefield. Usually, Submarines operate during the night. Germans mostly used advanced submarines which led them to attack US submarines effectively.
They called submarines as U-boats means underwater boats. submarines usually travel on the surface of the water and can go downwards to a limited extent. Submarines use a diesel engine for high surface speed and for long travel.