Mastering the time of tide occurrence and the water depth at high and low tide is an important condition to ensure the safety of ships sailing, entering and leaving ports, passing through narrow waterways and shallow waters. It is also an important factor that must be considered in the construction of military ports and aquatic airports, hydrographic survey, mine clearance, life-saving salvage, construction of coastal fortifications, organization of landing, anti-landing operations and underwater engineering construction. In the famous Normandy landing, when the allied forces made the landing plan, considering the tidal factor, the army chose to land at high tide and the navy chose to land at low tide. Because the tides of the five beaches are different, five different landing times are stipulated.