Depth control is done with an air-filled balloon and a Lego-compressor. Steering is done by turning the propeller direction with the help of linear magnetic coupling. Otherwise it's more of the same as before. Swimming pool and lake tests at the end. Enjoy!

Specs:
Displacement: 2.35 kg (5.2 lb)
Test depth: 6 m (20 ft)
Hull: glass jar (IKEA 365+ 1.7l), plastic lid
Balloon: latex water balloon for kids
Motors: 2x Lego PF L-motor (88003-1), 1x Lego PF Servo motor (88004-1)
Compressor parts: Lego pneumetic pump small V2 (bb0875), Lego pneumatic switch (bb0874), Lego Gear 24 Tooth Clutch (60c01), Lego Hose Pneumatic 4mm (21825)
Magnetic couplings: K&J Magnetics D34-N52 neodymium magnet, TapeCase 423-5 UHMW Tape
Propeller: Lego Propeller 3 Blade with 24t Gear (2740c01)
Radio control: 27 MHz controller dissembled from a toy submarine (Zantec Mini RC U Boot), L298 H-bridge to drive motors
Power supply: 9V Lego battery box for the motors, 3.7V Li-Po for the radio
Pressure sensors: Lego Manometer (64065), Jolly Logic Altimeter One

Note: The depth control I use here is called RCABS or Recirculated compressed air ballast system.

Previous subs:
1.0 piston ballast for depth control https://www.youtube.com/watch?v=tGEZApd9MMk
2.0 propellers for depth control https://www.youtube.com/watch?v=MdfUSNzc0Xk