Changelog for South China Sea update (added 21 May 2018):

South China Sea Campaign
* An all new campaign takes you to the warm waters of the Pacific where you'll take on the People's Liberation Army Navy of China in an attempt to maintain naval control and bring stability to the region.

New Player Submarines
* By popular demand, the formidable Seawolf class is now playable along with the Los Angeles Flight 2 and Flight 3.

Crew Voices
* Adding to the tension, immersion and putting you firmly in command, your crew now call out warnings, updates and verify orders you've given.

Point and Click Controls
* We got a lot of feedback about the controls and listened to what players wanted, namely a full point and click interface with tool tips to command your submarine. So we added it (and made it fully modifiable to build the user interface you want).

Neutral Shipping
* Not every contact is a target anymore! Fishing trawlers, container ships, tankers and whales roam the ocean making it crucial to correctly identify your targets before firing on them.

Improved Terrain, Cities and Air Bases
* The terrain system has been completely overhauled to improve performance and visual quality. In addition, urban areas, cities, all new port facilities and air bases have been added, many of which may well be targets for your land strike missions.

Ship Recognition Manual
* Can't remember the difference between a Kanin and a Kashin, or a Luda and a Luhu? You won't have to with the in-combat ship recognition manual, a comprehensive encyclopedia of the various ships and submarines outlining their capabilities, sensors and weapon systems.

New Vessels, Aircraft and Weapons
* Over 35 new vessels, mostly comprising the People's Liberation Army Navy as well neutral shipping, have been added in conjunction with new weapon systems and aircraft to support them.

Vertical Launching Systems
* Available on the Los Angeles Flight 2 and 3, these batteries of missiles let you stock up on additional anti-ship or anti-land missiles which can be fired in rapid volleys.

Oil Rigs
* Similar to neutral shipping, oil rigs are also dotted about the oilfields of the North Sea and South China Sea.

Changelog for Patch 1.15g (added 17 August 2018):

US Navy Ships
* Two ships of the United States Navy have been added, the Belknap class guided missile cruiser and the Knox class frigate along with the Seasprite helicopter to provide air support.

More Player Submarines
* To give these US assets someone to tangle with you can now play the Soviet Charlie I, Alfa and November as well as the PLAN Han classes.

Quick Mission Editor
* Jump into the Quick Mission Editor to create skirmishes with the submarines, ships and aircraft you want to face off against. Play in the North Atlantic/Norwegian Sea theatre or the South China Sea/Pacific theatre as US, Soviet or Chinese nuclear submarines.

Medals for Soviet Navy and PLAN
* Medals for the Soviet navy and Peoples Liberation Army Navy have been added to help the modding community create full campaigns featuring the new official playable submarines as well as numerous additional ones they've already added to the game through mods.