For no particular reason, I've been looking at the 1977 Traveller skill tables. Putting aside the weapon skills, a few thoughts on general skills come to mind:
Out of 23 listed skills, there are three which are open to just a single career; Ship's Boat (Navy), Forgery (Other), Steward (Merchant).
Forgery and Steward makes some sense restricted to their particular careers. Ship's Boat seems odd though; I would think merchants and maybe scouts occasionally have to buzz around the solar system rather than jump through interstellar space. Of course the 1981 rules fudged/fixed this by allowing Pilot (with appropriate penalties) to be used in place of Ship's Boat. But still ....
Each career has from 10 (Other) to 14 (Merchant) skills available to them.
Looking back to the first point, maybe that's why Merchants don't get Ships Boat. They're already at the top of the 'range of skills available' list. Maybe it was a game balance decision? Still sucks for Scouts though. But they usually die in character generation anyway ...
Every career qualifies for Computer, Electronics, Mechanical, Medical.
I'm sure this says something regarding assumptions of how the game is played, or the default setting. Not sure what though; things break frequently, including the characters? Note that if your Traveller group is missing any of these skills, there must have been some sucky dice rolling involved.
Marines and Army look pretty similar when it comes to skills.
Well duhh. Differences are minor. Army qualifies for Air/Raft and Forward Observer, while Marines can get Vacc Suit. Which makes perfect sense if you follow the assumption that Marines specialize in ship boarding actions, and Army are the ground-pounders.
Navy can get Forward Observer?
Directing orbital bombardment? Schlepping along with the Marines when the poor jarheads have to get their boot's dirty planet-side? Some early draft of starship combat where FO was required? I'm probably over thinking this one.
When it comes to shady dealings, the difference between Merchant and Other careers is slim.
Both Merchant and Other have a lock on most of the dodgy skills; each get Bribery and Streetwise, and Other adds Forgery to the mix. Which goes to support the assumption (never really spelled out anywhere in the rules) that Other is a criminal underworld career; and suggests that Merchants are more smuggler than CEO.
No Gunnery for Marines
I like to think of my Marines as Royal Marines, who traditionally supplied the gun crew for one turret on a circa WW1 Royal Navy battleship. Not gonna happen with this skill list.
No Admin for Scouts
And we trust these guys to make our star charts and record data on the known universe? Oh well, they usually die in character generation anyway ...
No Leader or Tactics for Navy
Seems like this would be a given for a military career. But again that bumps the total available skills up high for Navy. And if you follow that line of thinking too far, Navy Marines and Army all start too look pretty much alike.