 Complete the following phrase:  Invasion by sea is the use of a body of water to facilitate the entry of armed forces into an area, often a landmass adjoining the body of water or an island. This is generally used either in conjunction with another method of invasion, and especially before the invention of flight, for cases in which there is no other method to enter the territory in question. Arguments in favor of this method usually consist of the ability to perform a surprise attack from sea, or that naval defenses of the area in question are inadequate to repel such an attack. However, the large amount of specialized equipment, such as amphibious vehicles and the difficulty of establishing defensesusually with a resulting high casualty countin exchange for a relatively small gain, are often used as arguments against such an invasion method. Underwater hazards and a lack of good cover are very common problems during invasions from the sea. At the 