Answer:
The buoyant force increases as the submersible enters the water, and it remains constant after the submersible is completely immersed.
Step-by-step explanation:
The buoyant force acting on an object is given by:

where
is the density of the liquid
is the volume of the object immersed in the liquid
g is the gravitational acceleration
From the formula, we see that as
increases, the buoyant force increases as well. Therefore, as the submersible is lowered into the water, the buoyant force gradually increases (because the immersed volume increases); however, when the submersible is completely immersed,
no longer changes, so the buoyant force remains constant.