When the Alterra space exploration no-weapon hippie division won't stop coming back in pieces or feces, it's up to the Alterra military research division to save the day. Or at least blow something up. Contrary to common believe, Alterra managers do like exploding things as much as the next person. Unless it's Alterra assets exploding, then possibly less so.

Thus introducing the certification-free edition of one of Alterra's most successful sub-aquatic obliteration vehicles, the Echelon.
While it doesn't sport the same cool black paint or doomsday arsenal as its deadlier sibling, it's still a step up from the typical Reaper-mouth-sized coffins normally available to Alterra personnel. You're welcome.
In a nutshell:

• Exceptional, boost-driven maneuverability with leapfrog capability.
• Smart onboard holographic projection of virtual environment with target lock and status recognition.
• Rated for a lifetime of 30 years, a built-in nuclear battery provides a low but steady energy supply.
• High resilience against any damages.
• Self-healing capabilities.
• Smart torpedo support with intercept capability and safety mechanics.
• Onboard torpedo production, using materials filtered from the drive water flow.
• Smart railgun support with aim assistance and intercept capability.
  

Please be aware that Alterra is not responsible for accidents resulting from inappropriate speeds, particularly when leapfrogging out of the water.

How to use it

• Get the Vehicle Framework mod.
• Make sure Nautilus and BepInEx are up to date.
• Get this mod.
• Build a Mobile Vehicle Bay.
• Get the resources and build the craft.
  

Alternatively, use console commands: 'spawn echelon'.

V1.3.0: Railguns
I hinted at this from time to time that I was never really happy with how the torpedoes ended up. Rather than replace them, however, I now added railgun modules. Both torpedoes and railgun can be fitted to the same sub, but only one can be active at a time (the weapon quickbar items are now toggleable).
Railguns behave very differently from torpedoes:

• Firing the railgun requires charging it first. Hold the fire button for one second and it will auto-release once automatic aiming is complete.
• Shots fire in a straight line and hit everything on their path with massive amounts of damage.
• MK1 deals 2k damage, MK2 4k, enough to kill everything with 2 shots.
• MK1 railguns have a limited auto-aiming assistance, MK2 will rotate the sub from every direction if possible.
  

Localization
With v1.2.5, the first batch of different language versions was added. Languages will be added as players demand them and/or as users wish to provide them. Currently the following languages are defined:

• French (Thanks to Noro)
• Turkish (Thanks to EgeK)
• Polish (Thanks to Royalty)
• Spanish (Thanks to RagnarokOne)
• English
• German
• Danish
  

If you feel like you can contribute to the localization process and want to be listed here, feel free to contact me on Discord (iconic_fox) or create a pull request on Github (the language files are here)

Important Changes 1.1.0 Moving Forward
With v1.1.0, the first batch of modules were introduced. This currently affects weapon firing, nuclear battery output, boost speed, and self repairing.
The base sub currently fires no torpedoes or railgun shots and does not self-repair. You will need to create the corresponding upgrades using the VF Fabricator:

Most modules come in three tiers, mark 1 through 3, some only 1 and 2, increasing their output, often exponentially. The highest equipped module takes effect. Echelon-specific modules do not stack.

With v1.1.1, nuclear battery upgrades (Mk1 and 2) were added as well as crush depth reduced to normal levels (will now use regular VF depth modules).
With v1.2.0, self repair and drive modules were introduced. While the base vehicle can still boost, it cannot self-repair.
With v1.3.0, railgun modules were added. Like torpedo modules, they need to be built, equipped (and selected if you also have torpedoes on the sub) before being able to fire.

Compatibility Concerns
For the most part, this mod coexists with others. You will find the mods that add third-person to other subs will not work here at best, and produce oddities at worst. Best not to use them while using this sub.
I also found that mods that provide free look while in the cockpit of a sub (e.g. Cockpit Free Look) do not work well with the way this mod treats the camera.
If you have that one, you need to change either the keyboard shortcut of this or that mod to relinquish the F-key. Since the vehicle framework normally also uses the F-key (but not in this case), I felt it appropriate to keep the F key.

Control areas:
The sub can be entered from the top (see marked hatch).

The rear section, where the glowing energy charge display is located, can be used to access the one battery used by the sub.
It can be replaced by a full and/or ion battery.

Modules can be accessed at the arrow symbol down front:

Module compatibility is somewhat untested. The default vehicle framework storage expansion now does work (Echelon 1.3.1+) and can be accessed via the quickbar, as does Better Vehicle Storage (use Vehicle Framework v1.7.0 or newer).
Depth modules also work and are now mandatory if you wish to dive deeper. Other modules may work but have not been tested.

Visual Enhancements:
The Echelon encourages a third-person camera at all times, however does now also provide a first person perspective (zoom all the way in via mouse wheel or configured keys). Use the mouse (or controller right stick) to look around. Depending on the current mode, the sub may or may not orientate accordingly.
The sub continuously monitors its surroundings and marks relevant targets in up to 500m distance (though the game may not actually spawn creatures at 500m away).

This target display shows the current health as a circular bar around targets. Particularly strong or otherwise dangerous targets will cause it to pulse.
The bar changes colors depending on how healthy that target still is. These rings can be limited or completely disabled in the options menu (Target Health Marker Display).
Depending on settings, text will appear next to each target marker, showing its name, health, speed, and distance.
This feature can be disabled or limited via the options menu (Target Text). Although I could not test it, I believe this to be the most VR-problematic feature.
If you play this in VR, you may have to disable on-screen text entirely.

Environment Target Arrows
While using the 3rd person camera, AR arrows are shown to highlight dangerous and/or critical targets in the vicinity.

The arrows will become more apparent as the target gets closer and start to pulse within 100m distance.
The color depends on the threat-assessment: red arrows indicate a critically dangerous target, yellow "just" dangerous.
As of the time of writing, only shockers are classified as dangerous. Aggressive leviathans and warpers are considered critically dangerous.
Depending on settings (Target Arrows), these arrows can be limited to critically dangerous or disabled entirely.

Target Focus
Every target marker on screen can be focused on by pointing the camera at it. If any torpedo module is equipped, focused targets have a second rotating ring inside.
This is the currently active target, which will be locked by any fired torpedoes. If no target is currently focused, the animated ring will appear near the crosshair. Torpedoes fired in this mode will simply try to reach the closest ray intersection beneath the crosshair. If there is none, the target is a virtual point 500 meters forward.
Without torpedo modules, focused targets will become less transparent but not have a rotating ring. There will also not be a forward marker.

Energy Display

The sub has an energy bar on the rear section that shows the current battery level and changes. It will change color depending on the current charge.
Animated bars on the outside visualize the current charge change speed.
If the battery charge falls dangerously low, pulsing yellow or red backgrounds will appear.

Controls
By default, the sub is in direct control mode, which means it will orientate itself to always point in the direction you're currently looking if it can.
Similar to other subs, the Echelon will move in all 6 possible directions depending on input.

• The Mouse Wheel can be used to zoom the camera. If you zoom in all the way, you'll get a mostly 1st person camera. Likewise, zooming out from there will return you to the normal 3rd person camera. If you don't use a mouse, you can bind controller buttons to zooming in the mod options menu.
• The Run-key (as running while not swimming, possibly Shift) will enable boost mode, pushing the sub much faster through the water.
  By default, this key is toggle boost-mode but this can be changed in the settings.
• The F-Keyboard key (configurable) can be used to switch into free-camera mode.
  While in this mode, the sub will not auto-align to the look direction but instead maintain its current heading.The inputs, normally used to strafe up/down and left/right, are now used to alter its heading.The sub cannot strafe while in this mode.
• The left-hand trigger (mouse left button on mouse/keyboard) will cause the sub to continuously fire torpedoes at whatever you've targeted or are looking at (see previous chapter) as long as at least one Torpedo Upgrade has been installed.
  The frequency depends on the level of that upgrade. Torpedoes are fired alternatingly from the left and right tubes. While firing, the sub's battery will be drained 2 energy points per second.
• F7 opens/closes the debug console. It just prints some status values onto the screen. It is disabled when disembarking and not re-enabled unless you press F7 again after boarding.
  

Power Management
The Echelon features a nuclear battery that provides a continuous charge to the regular battery. The energy output depends on the presence of any nuclear battery upgrades. Without any, the recharge rate stands at 0.4 points per second. Mark 1 battery upgrades double this value to 0.8, Mark 2 to 1.6 points per second.
The sub detects low and critical power states.
If the sub battery level drops below 2%, boosting and torpedo firing are no longer possible, but self-healing (if available) will continue. At 1%, the sub goes into critical battery state, disallowing self-healing but still providing normal maneuverability.
The battery should not be able to die in this state.
If the battery, however, does die, oxygen production and any mobility will shut down. Once dead, the battery can no longer be charged (this is a built-in feature of the game) and must be replaced.

Boosting
When using the run-button while in this sub, the sub will go into overdrive. It will consume more energy than normally but it will also move much faster. The level of acceleration depends on the level of any installed drive modules. Without any module, boosting is possible but only gives you +30% speed when compared to non-boosted. The boost applies to all directions except reverse while active. Please note that air poses much less of a drag resistance than water, so moving very fast out of the water converts your sub into an artillery shell, hopefully minus the explosion upon reentry.

Self Healing
If damage to the sub is detected while any self-repair module is installed, that module will activate. While active, a green patterned glow will surround the sub and illuminate dark areas.

The speed, at which the sub heals itself, depends on the level of the module equipped. While active, healing will consume 1 battery charge point per second.

Torpedoes
Early on, it was decided that torpedoes would be the weapon of choice for this sub. As it turns out, that was not the best decision and may change in the future. Subnautica has a very inconsistent way of handling terrain colliders outside the immediate range of the player. After around 50 meters, there is no guarantee that the colliders even exist or that they align with the visual representation.
Therefore, by default torpedoes will ignore terrain colliders if fired at a locked target. If fired straight ahead without target, they will collide with the terrain (or any invisible collider they encounter). If randomly exploding torpedoes are starting to drive you nuts, you can disable all collisions in the options menu (Torpedo Terrain Collisions). Or, if you feel like you're not nuts enough yet, you can enable it for all torpedoes. Note, that after 100 meters or so, torpedoes will always clip through the terrain, regardless of this setting, because the game does not provide any colliders there.

If a torpedo is about to explode within damage distance of its origin sub, it will not explode and just disintegrate. So, if a reaper got hold of you, firing torpedoes at it will do nothing. The torpedoes will be shot, but they'll just disappear because you're too close.
Do not get grabbed by anything or just wait it out.

Some notes regarding concerns:

• This mod is unbalanced (when fully upgraded)
  Yes. Its very nature is inherently unbalanced if upgraded. The game normally wants you to run and hide from its predators and be punished if you don't.
  The biggest weapon it gives you is a PRAWN hand.
  This mod takes this natural pecking order and turns it upside down. Fully upgraded, the Echelon is nothing short of a near-indestructible reaper shredding machine.
  With high maneuverability, environment awareness, self healing, and rapid lethal torpedoes, its core design philosophy contradicts the game's normal limitations. If you don't like escaping those limitations, either don't install some upgrades or steer clear.
• Using the sub, I can float through ruins even if there is no water there
  Noted. Right now I haven't the faintest why this happens or how I can prevent it.
  I can only assume that the game devs never anticipated small subs to even reach those depths.
  There appears to be some water current that tries to prevent entry of the lowest ruin but the Echelon is just too fast for that.
• Can I use your stuff?
  This uses the MIT license. Knock yourself out. If you sell it successfully, consider hiring me. That being said, I would advise against simply copying this mod and claiming it was yours.
• Are you nuts to make this?
  Professionally so.
  

Code and compiled media: Echelon Github

Discord contact: iconic_fox