Gravitic Cavitation - what a wonderful term, consider it borrowed
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What do you mean by traditional?
IMTU I have for a long time used the following model for how the book2/HG m-drive operates.
The m-drive generates an inertial dampening field around the volume of the ship- a gravitic bubble or cavity to use your idea- which reduces the inertial mass of the ship. A small fusion exahust from the reactor can then be used for thrust.
The higher the m-drive rating then the greater the mass reduction and hence the greater the acceleration.
The MT/T20 thruster plate operate by pushing against the curvature of space/time.
In TNE there are contra grav lifters, acceleration compensation and HEPLAR m-drives.
In all models since there is some form of gravitic interaction (even if it's just the inertial compensation and artificial gravity) there may well be a disturbance that some sort of gravitic sensor could detect. Some versions of Traveller have such sensors, others do not. It all depends upon how you want the sensor tech to have developed IYTU.
Personally I stick to the active/passive EMS system, I don't allow shoe box sized neutrino or graviton detectors and use a T2300/TNE sensor system for ship to ship combat which makes it more like a sub- hunt because that is what I prefer.