Crushing Depth and submersibles

 In my spare time, I love worldbuilding and writing down settings, that may or may not be used for future campaigns. For many of these, I need to design new vehicles such as flying ships, teleporting mecha, or just planes. That, actually is why I so often use GURPS Spaceships system in non-traditional ways. for example, For one of my settings I wanted to design a whole lot of water-related vehicles, from cruisers to submersible planes. And its during this design I found out weird inconsistency in Crushing Depth rules. Let's demonstrate it on this Salachi Submersible Fighter.

RM SF-01 Slachi (TL9)

Salachi is intended as submersible fighter for multi-environment fighting. Being able to start off from underwater and even hunt submarines with its many torpedo launchers. Uses streamlined SM+4 hull

Front
1-2 Metallic Laminate Armor (dDR 2)
3-4 Major Battery ( 2 fixed 16 cm Torpedo Launchers )
5 Tactical Comm/Sensor Array (comm/sensor lvl 4)
6 ECM 
c Control Room (One control station, C6 computer, comm/sensor lvl 2)

Center
1-2 Metallic Laminate Armor (dDR 2)
3-4 Major Battery ( 2 fixed 16cm torpedo launchers)
5 Fuel Tank (MHD Fuel)
6 Submarine Ballast Tank
c MHD Turbine (2 PP)

Rear
1-2 Metallic Laminate Armor (dDR 2)
3 MHD Turbine (2 PP)
4-5! Reconfigurable System (Jet engine [MHD Jet], Screw Propeller)
6 Maneuver Enhancement (Underwater)

The fighter is streamlined and is winged. [Uses homebrew Jet engine that uses Power Points instead of Fuel]
Features: Emergency ejection, Stealth Hull

Top Air Speed is 3,500 mph, Move 20/1750 (which may or may not be too much for my taste),
Hnd/SR +4/5

Underwater Move 1/10 
Crushing Depth... Well, let's calculate (2 x 150)/30 = 10 yards of depth. 

This depth aligns somewhat with submersible plane depths, but not submarines. We can attmept to mend this problem with Volume based dDR rules, which make our fighter have dDR 2,4... whichstill rounds down to 2, so no that is not what we are doing. For now, let's leave Salachi with its 10 yards of depth.

Our next subject will be more... demanding

Kavouras Superdeep Undersea Explorer

This is a vehicle, designed to explore ocean's bottom, underwater fissures and other environments, normally unavailable for normal submarines. Considering it's purpose we need it to have the greatest crushing depth we can squeeze out of it.

Front
1-3 AML armor 
4-5! Robot Legs
6 Science Array 
c Control Room

Center
1-3 AML Armor
4 Robot Arm
5 Major Battery (fixed 16 cm Torpedo launcher)
6 Submarine Ballast Tank
c MHD turbine

Rear
1-3 AML Armor
4-5! Robot Legs
6! Screw Propeller

Now, we skip directly to calculating crushing depth...

aaand, for an SM+4 submersible that is almost 50% armor, it has only 45 yards of crushing depth. Considering, we want this thing to explore the oceans bottom, which is around 3K yards deep on average - this is not nearly enough. 

So, what do we do? My first proposal would be this feature:

Pressure Hull - the vehicle is optimized to operate in high pressures, increasing its Crushing Depth by the factor of 10. This feature can be taken up to two or three times. 
This feature allows to emulate most actual submersibles, but will sometimes require a little stretch in one or other direstion

For example, with two levels of this feature, Kavouras now can reach 4500 yards down, which we will stretch somewhat higher to 5K yards
and our Salachi now can dive to 1000 yards depth, lowered, somewhat to 700-800 yards - normal depth for submarines today.

The normal formula can still be used to represent less adapted vessels trying to swim or operate in high pressure environments. The feature is free, but feel free to ask your players to pay money for levels higher than TL-6. My suggested price is the same as for Dynamic Chameleon feature (but only because I'm too lazy to go into details about actual prices of pressurized hulls)