To solve the volume of water in units of cubic meters, we are going to convert first all units in terms of meter.
  
 Let us say that the dimensions are:
 length l = 4.40 nautical miles
 width w = 3.90 nautical miles
 depth h = 20 fathoms
  
 Converting the dimensions to meters:
 l = 4.40 nautical miles (6076 feet / nautical mile) (1 meter / 3.28 feet) = 8,150.73 m
 w = 3.90 nautical miles (6076 feet / nautical mile) (1 meter / 3.28 feet) = 7,224.51 m
 h = 20 fathoms (6 feet / fathom) (1 meter / 3.28 feet) = 36.59 m
  
 The volume of a rectangular prism is:
 V = l w h
 Substituting the values:
 V = (8,150.73 m) (7,224.51 m) (36.59 m)
 V= 2,154,330,380 cubic meters