Since creating new traveller progressions seems to be all the rage now, here's my own attempt at it (and it does branch off, like several other fan progressions):
Base Card:
Grunt:
+3 Actions
If you have your Admiral token, +1 Card.
If you have your General token, +1 Card.
When you discard this from play, if you have no remaining Actions (Actions, not Action cards), you may exchange this for an Ensign. If this isn't the only Grunt you have in play, you may exchange it for a Lieutenant.
Cost: $3
Action - Looter - Traveller
FAQ: You discard cards from play one at a time, so if you have two Grunts in play when cleanup starts, you can only exchange one into a Lieutenant, because when you discard the 2nd one from play, its the only Grunt you have in play.
Navy Progression: Theme: Durations
Ensign:
Now and at the start of your next turn:
+2 Actions
+1 Buy
+$1
Each other player takes his -$1 token.
When you discard this from play, if you didn't buy any cards costing $5 or less this turn, you may exchange this for an Admiral. (This is not in the Supply)
Cost: $5*
Action - Attack - Duration - Traveller
Admiral:
Take your Admiral token.
Now and at the start of your next turn:
+2 Cards
+1 Action
When you discard this from play, put it on your Tavern mat. At the start of your turn, you may put this into your discard pile for +1 Card and +1 Action. (This is not in the Supply)
Cost: $8*
Action - Duration - Reserve
Army Progression: Theme: Choices
Lieutenant:
Reveal the top 3 cards of your deck. Put any number of them into your hand and discard the rest. +$1 per card discarded this way.
When you discard this from play, put any number of Grunts you have in play on top of your deck. If you put at least two on top this way, you may exchange this for a General. (This is not in the Supply)
Cost: $5*
Action - Traveller
FAQ: You cannot exchange a Grunt for another Traveller after putting it on top of your deck, as you never discarded it from play.
General:
Take your General token.
Choose one: Gain a Duchy; or gain a Gold. Either way, put it into your hand.
Each other player gains a Ruins and a Copper.
Cost: $8*
Action - Attack
FAQ: Generals are always used when Grunts are, so Estates are worth 0VP whenever Grunts are in the Supply.