Many many years ago I spent a day as a safety diver for the International Submarine Races and was impressed with the engineering and speed some teams were reaching on pedal power.
To control conditions the race is run in the Surface Warfare test tank, that is cold dark water and since you need to stay in place you get chilled fast!
The subs follow a line of chemlum sticks but since most crews are overbreathing as they speed down the course they fog up the mask, can’t see the chemlume sticks, get off course and crash into the wall at speeds up to 7 knots!