Which plane is described as always changing in relation to Horizontal and Vertical Planes?

The deck plane is described as always changing in relation to horizontal and vertical planes because it adapts based on the ship's movement and its orientation with respect to the water surface. As a ship navigates, it pitches, rolls, and heaves, causing the deck's orientation to alter constantly. This characteristic is vital for accurate targeting and fire control operations, as weapon systems must account for the dynamic nature of the ship’s stance when positioning and firing.

Understanding this concept is crucial in fire control operations, where precision is paramount. The other planes mentioned have more specific and fixed definitions, such as the normal, ship base, and vertical planes, which do not exhibit the same variability as the deck plane does when the ship is at sea.