You likely mean to say SS for Submarine?
Also, the fastest underwater Sub in the game is the U-2501 at 28.4 knots (with Speed Flag). The Enlarged Propeller commander skill used to offer additional speed when at low Depth Timer, but that no longer affects Underwater Maneuvering.
Six matches is rather low in a statistical sense, so you should consider continuing your experiment to a higher number. Some say 30 is high enough to use as a sample size, but I think 100 is more commonly used as an off-the-cuff baseline.
This is the best reason for those additional games. When confronted with new mechanics and situations, many players don't have the built-in responses mapped out yet and you can see outlier situations especially in low-count assessments. It might be on Game 19 or Game 45 where you encounter someone that has a really strong understanding for what to do and how to execute on it which can radically alter your view of what is and isn't possible. The only way to reach that experience is through continued play.
To relay my own experience on this, I was asked why I would give advice on what cruisers/destroyers/battleship players could do in the face of a CV attack while I was still rather new to the game and didn't have much experience with those classes. My response was "because I've seen good players use these tactics against me many times and they were very effective." I may not have been able to translate them into my own play due to inexperience, but there are very talented players that will present new obstacles/challenges which are easy to identify and are worth taking some time after the match considering.
This is where playing Submarines for more battles can be helpful. You will run across other players that have better understandings of the matchup and you can learn from experiencing those situations.
Submarine Surveillance is a submarine consumable which detects enemy subs at Max and Periscope Depth.
Hydroacoustic Search is a surface ship consumable which detects enemy subs at max-range while at Surface and Periscope Depth, and within 2km at Max Depth.
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