Most operation is done at periscope depth so we can see the tip of the mast.
I like clear water so I can see down at least 5'.
This is not always possible.
After a rain storm the waters tend to be muddy.
When the water is murky, I hope I have enough feel for my boat to run at about 18" so I can come up a little and have the mast break the surface of leave the small wake.
Also, by running near the surface and seeing the mast or wake you know what the direction is and you know your speed then you make a run using perceived time and make turns where yu think you are and after a few moments...I started tosay minutes but that would be too long in most cases.. you break the surface to see how close you calulated your position.
Just like the real thing.
And most of all hope next time the water has cleared up.
The stress of running in dirty water can be a lot to handle.
Never know if you might run in to the weeds or submerged junk.
Many years ago, was watching a 5' sub operate and it did not return.
Even after exhausting it's batteries.
Three years later the city drained the small lake to clean it u0p.
Sub was found not 30 feet from where the operator was standing.
The sub had run in to a grocery store shopping cart and couldn't get out.
The sub has the owners name inside and he got it back.
Was a bit of a mess.
I do not know what happened after that.
SSBN 598 - blue/nuke trained IC/forward