The clue may be in the differences in FGMPs as TL progresses. The first examples require Battledress for recoil and radiation protection, while the later examples do not.
This suggests that the process of getting that packet to fuse is a matter of a fraction of a second, and the earlier FGMPs then eject it toward the target with a mighty kick and a lot of leakage. Usage suggests that it is still fusing as it leaves the weapon in the earlier models, but, as is the way with fusion, may no longer be quite that energetic by the time it arrives on target. Still a lot hotter than mundane plasma, though, so the damage difference is justified.
The later examples are better shielded, have better containment in general, and better handling. They still require recoil compensation, but no longer need radiation protection external to the weapon. The recoil compensation is moved internal to the weapon (plenty of power, after all), and the fusing point is fully contained. When fired, it spews that same "fresh from the sun's maw" high end plasma, but the gamma radiation that escapes with the plasma is either stopped or lensed to stay with the plasma packet. Aside from the occasional unfortunate air molecule the shot isn't irradiating everything down range, just what it hits. Since the gamma *source* remains in the weapon and isn't running full time, 99% of the residual radiation will be scatter from the target point.
What we see in the several books that document Imperial equipment is a "modern" picture of TL15 Marines with FGMP-14/15, while the Imperial Army (as seen in GT: Ground Forces) uses gauss weapons. Certainly the scenario in CT Spinward Marches Campaign makes a BIG deal of missing HE weaponry. What we don't see is the picture 400 years ago, when the FGMP-14 was top of the line. Line troop doctrine was probably a bit different then...
While this is true in (at least some) former Traveller editions (CT and MT are the only ones I know with some level of detail, TNE and T4 with quite less level, and nearly nothing about others), where PGMP TL12 and FGMP TL 13 needed BD (due mostly to their high recoil) and latter versions didn't, in MGT, the entry about FGMP (Core book, page 102) doesn't discriminate among its versions (TL 13, 14 and 15) about this radiaton protection need, so it seems PGMP doesn't need BD (if you're strong enough to sustain its recoil), while FGMP does, regardless of the version.
...specifically the "regardless of size and type" note. As I recall it the prohibition was against WMDs, solely, and iirc only when used (not simple possession) against forces on a world (but fine for space warfare).
Which suggests that the rule was written with WMDs (down to nuke artillery rounds) in mind.
Excuse this poor ignorant, but, what WMD stands for?
I'm sure I recall some CT era adventure(s) or JTAS news briefs with locals and mercs using limited nukes without Imperial boot-stomping. And JTAS news briefs or planet backgrounds that talk of wide spread nuclear war on planets which the Imperium does frown on but suggest they don't act on simple possession (it's not something that could be hidden from the resources of the Imperium to check and monitor).
I recall the Amber Zone
Thunder on Zyra (JTAS 11, Page 6-7), where some mercenaries have bought a pair of nukes, where it says they only dared to do that because Imperial attention is centered on the FFW and they feel it won't intervine on time, so hinting they fear Imperial Intervention on that fact.
I also recall another AZ (for MT, this time) on a challenge (sorry, I cannot find it now exact reference), where a megacorp is hiring mercs to crew tree nuclear powered ships (a CVN, a CGN and a SSN) on Amaranx, and they fear imperial intervention due to importing nuclear 'weapons' and tech to a TL 6 planet, even fearing to lose the contracts achieved if latter the Imperium finds about it after the fact.
Of course, this last AZ gives us even more to concern: if fision powered nuclear ships are so considered, what about fusion powered grav carriers or tanks?
Of course one could put this all down to evolution of the game...
Nukes are fine for everyone, even simple free-traders (CT B2 missiles have to be nukes for the damage when compared to CT B5 missiles which must be something else)
Big nukes are bad except for the Imperium.
All nukes are bad except for the Imperium.
Some personal weapons that were not radiation hazards are now.
Said same personal weapons are bad except for the Imperium.
In OTU it seems the minimum restriction is the one I underlined, as Imperial Rules of War stand.
It's Striker Rule 78 (dunno if it was used before). However it is qualified by a rationale:
"...because of their extreme destructive powers and the possibility of great damage to the civilian population."
About
extreme destructive powers, in MGT, if you compare the damage a Fusion Bay (there are no fusion turrets) compared with nuclear misiles in starship combat, then Fusion weapons are even more destructive (5d6 + rad vs 2d6 + rad).
About radioactives heavy elements fallout, we must remember most high tech nukes are laser tiggered fusion devices, so no heavy elements are included, and, while they are supposed to irradiate, fusion reaction doesn't contaminate as much as fision weapons do.
AFAIK (I'm not an expert) there's more such contamination (not radiation) in the use of DU munitions today that a fusion explosion without fision triger would produce.
