YMMV / Cold Waters

• Demonic Spiders:
  • ASW helicopters. Every enemy warship larger than a frigate carries at least one. Each one carries at least one air-dropped homing torpedo that they can drop right on top of you, they'll follow you around with their dipping sonar and MAD gear, letting every Russian ship know exactly where you are, and there's not a goddamned thing you can do about it, since pre-2010s submarines have no anti-air capability, as since jets became a thing hand fired flak guns became practically obsolete. Even if you sink their mothership, they'll still hound you for hours, preventing you from exiting to the strategic map (luckily, there is a time-compression option). If you're lucky, you'll sink the ships carrying them before they can launch—assuming they weren't patrolling already.
  • When the game first launched, land-based ASW aircraft were like the helicopters, to unrealistic degrees. They'd harass you in areas beyond their actual range limit and in areas where NATO realistically should have had air superiority. Their sonars were also overpowered, allowing them to far too easily detect the player's submarine. Fortunately, patches altered their ranges and sonar capabilities, making the much less of a threat. Then the South China Sea campaign came out and, since it involves so much shallow water combat well within Chinese air cover range, made them demonic again.
  • Diesel subs. They're just so damn quiet and can easily sneak up on the player.
  • Any ship with cruise missile launched torpedoes. Think your sub is out of range of enemy counter fire? If one these ships is around, think again. And because missiles move much faster than torpedoes, you'll have much less time to react than if they fired a torpedo over the side.
• Difficulty Spike:
  • Because the technology available to both sides is much less advanced, the North Atlantic 1968 campaign can be much more difficult than 1984. While it does help some that Soviet sensors are less sensitive, their torpedoes are not as capable, and their subs are louder and slower, you have all those same disadvantages. Of those disadvantages, your torpedoes are significantly worse.
    • Your first option is the Mk 18 torpedo, which is basically the same thing that the US Navy was using 23 years earlier at the end of World War II. Although it's fast and the warhead is enormous and will sink pretty much whatever it hits, it can only be fired from 200 feet deep or higher, it's max range is only 10k yards, and damningly, it is not a homing torpedo. Once fired it will make one turn to the heading you specify, and then it will run that way until it hits something or runs out of fuel. This means it's utterly worthless against enemy submarines unless they're running on the surface. Against surface ships, any change in enemy course and speed after it is launched will result in a miss. It's also very loud to launch, so the enemy is likely to hear it coming. Thus, in order to realistically kill anything with it, you need to first risk detection by sneaking up to point-blank range, and then fire a spread at different angles to "play the odds"... which leads very quickly to running out of torpedoes entirely.
    • Your other option is the Mk 37 torpedo, which is smaller, electrically-driven and wire/acuoustically-guided. While this is good for hunting enemy submarines, as it is very quiet during launch and while running slowly with wires attached, it has a much smaller warhead and it may take more than one to sink anything but the smallest of targets. Moreover, its speed maxes out at 36 knots, meaning that it will have a hard time catching enemy nuclear-powered subs and it is completely unable to catch most Soviet surface escort ships.
  • The year 2000 South China Sea campaign is considerably more difficult than the 1984 North Atlantic Campaign, due to a combination of technology and geography. While you have access to more advanced subs, namely the Seawolf and 688i Los Angeles, the PLA Navy also has more advanced sonar and wired guided torpedoes. A lot of the combat also takes place in the shallow waters off the Chinese coast, making evasion trickier. There's also the size of the Pacific Ocean; getting to and from your home port of Guam for refit and resupply can easily cost you a mission. It's very easy to miss an invasion force heading to Taiwan or the Spratly Islands because of how close they are to the Chinese ports. There are also a lot more civilian ships, so an itchy trigger finger can cost you a command right quick.
• Genius Bonus: When playable Russian subs were added to scenario mode, American NPC ships were also added to provide opponents for them. If you look closely at their models in the in-game viewer (or in battle if you're gutsy enough to raise the periscope close enough to read them) you can see actual international signal flags flying from the yardarms. They spell out Foxtrot Uniform Charlie Kilo Yankee Echo Alfa Hotel^note FUCK YEAH
• Scrappy Mechanic:
  • Cruise missile strike missions are...less than intuitive. The Steam forum is filled with threads just asking how the hell they're supposed to work. Here's an example of a TLAM mission bugging out on The Mighty Jingles due to the use of an out-of-the-box tactic (eg. Sinking a civvie ship, then putting his sub on top of the sinking wreck to mask his position). It eventually became so bad that Killerfish patched it so the strikes are automatically considered successful so long as the player launches the appropriate number of missiles. Even then, the missions will still bug out sometimes.
  • The movement controls were not well received by simulation veterans, with the WASD keys being used for diving, rudder, and speed. Thankfully, Killerfish listened and a new set of controls were patched in August 2017.
• That One Level: TLAM strikes, for reasons noted above, and SEAL insertions. Both require the player to sail deep behind enemy lines with a depleted loadout of torpedoes (the only way to make room for the SEALs and their gear is to empty the torpedo room) and if you get spotted by an enemy recon plane or satellite, you can expect to have multiple hunter-killer groups on your ass. Being assigned to go to Arkhangelsk is the absolute worst, as it's on the White Sea inlet with only one way in or out, so if you're being hunted by HK groups you will run into them trying to get out.
  • Ironically, while the South China Sea's generally very shallow waters make many missions in the 2000 campaign harder than their equivalents in 1984, the advanced submarines available to you actually make TLAM and SEAL missions easier. USS Seawolf has eight torpedo tubes compared to the four on Los Angeles class, so you can execute a full eight-missile TLAM strike in one launch and run like hell, instead of having to launch one salvo, hide while reloading, and launch again. Those eight tubes also make it easier to defend yourself on SEAL missions where you have no spare torpedoes. The 688 flights II and III have twelve vertical launch tubes (for missiles only) in addition to their four torpdeo tubes, so you can keep your torpdeoes ready and launch Tomahawks at the same time, and have some antiship missiles left over for your SEAL delivery mission.
• Tear Jerker: Sinking below 400 feet (and therefore making you and your crew too deep to rescue) can be rather depressing to think about, especially after reading your XO’s final words to you.