I discovered Traveller in, oh, 1979 I guess. My friend and I found the game, the 3 LBBooks in the LBBox, effectively abandoned, on a shelf in the Chemistry/Physics lab/classroom at my school. Nobody claimed it, so we just took it.
We were already playing D&D (someone had the basic set, rather than "real" D&D that the "older kids" had), but we went with it.
So, we ran off and we would just roll characters. We had stacks of index cards (I think I still have those stacks somewhere).
Later, I would play the trader game with another friend. I wrote a program on my calculator to automate a bunch of it.
I also carried it with us on a school field trip and taught it to a teacher who was interested in it.
The Starship building, and world generation were always interesting to me, but what "hooked" me was Book 4, specifically the "Ironmongery" chapter. All of those weapons seemed so real. It wasn't made up laser blasters, this was the real stuff. I loved the Keith drawing of the trooper scout just inside. Rifle, pack, headset. Hi tech, but "real". High Guard helped cement it. Truth be told, I know there's a whole section on Navy careers in that book, but I can safely say I've probably never read it in detail. All about the hardware.
I've never played in a campaign. We "played around" with it, but never really played it. Never serious. I seem to recall an incident in an "old west" town (being as it was on a map we got from Boot Hill). We had the Grav APC, and a fellow came through the swinging saloon doors and said "Draw!", so we hit him with the VRF Gauss gun in the turret. I wrote a small program on the PET (we were in the computer lab, after all) to calculate the damage that turned him in to a red mist and the saloon doorway in to more of a round shape.
In all seriousness, I've probably played the game, as a game, running an adventure, 3 times total.
Once, with a friend, I think we ran Chamax Plague. I recall rewiring missile warheads and blowing them up, something like that.
Second time, at a game club, it was an adventure out of JTAS I think. We had to assault an "unassailable" asteroid to get some plans or something. Instead we ended up taking our mustering out money, buying several tons of cheap calculators, and selling them all to the population of the TL 5 world with the Religious Theocracy Government that the asteroid happen to be in the same system. We were "instant" zillionaires and the Ref was upset that we didn't want to risk our life attacking the asteroid for 10,000Cr reward. And, yes, I blame the Ref.
Third was at a convention, and it was a great adventure. Non-stop, lots of action. Save for the underwater city, it probably could have happened today -- but no matter it was a hoot.
I like the rule systems, the gearmongery, the crunchy bits trying to model the world of Man on a galactic scale without the hand waves, but, rather, a couple of tweaks. People like us, but with fusion power and starships.
I like the Imperium. I like the setting. I was STUNNED (literally) when JTAS #9 came out and the FFW started. That was Important information. I was saddened by the Rebellion. By the war. By the Virus. The billions upon billions dead.
So, I didn't really need to play Traveller, I sort of just lived it instead
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I'm waiting for T5, I've passed on T20 and MgT. I didn't want the 3LBB again in T20, and I just haven't liked what I've seen in MgT.