Submarines are underwater ships used by militaries around the world. This mega machine can be over 550 feet long and can carry up to 160 crew members on board. The fastest submarine, the Soviet submarine K-222, can reach speeds of over 50 mph! Young readers will love learning about this underwater mega machine. With approachable, informative text paired with full color photographs of submarines, readers will discover how submarines work and what makes them truly mega machines.