A quick test revealed that that gave the unit the ability to move on either ocean or shallow/river regions with impunity. While this reduces the unit’s ability to fight at sea, it also increases its ability to dominate the rivers, as the current ocean going elements are far better than the river ones.
Here’s an image showing a unit at Norfolk plotted to move via ocean regions, then up the river to Southern Illinois:

You can see on the bottom right it now has two types of elements in the unit.
Jim