As I read through, I'm curious what bits might be of interest from the later editions of Traveller. By and large, I'm inclined to stick with Classic Traveller, but if there's interesting bits from later editions, I'd love to hear more. Consider also that I have little to no interest in the OTU.
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Anything of interest in T4?
I definitely like the armor penetration rules for personal combat in T4. Each point of armor "eliminates" 1D of damage rolled (independent of the points on the die). If it is "rigid" armor, the armor point completely eliminates the damage die. If it is "flexible" armor, it reduces the die to a single point of damage. This simulates the "bruising" factor of armor like ballistic-cloth.
The variability in the amount of damage the armor eliminates (because it is reducing dice instead of points) also abstractly takes into account thicker and thinner parts of a suit of armor (such as joints vs. breastplate).
Under normal circumstances (there are specific exceptions), a weapon will not deliver more than 3D of damage to a person (after armor reduction) due to overpenetration. This, taken along with the above, also means that there is an implicit distinction between a weapon's penetration versus its damage delivered.
It is a simple, easy, and elegant little mechanic that abstractly packs in a fair amount of complexity.
And it is easy to import the mechanic into CT.