See that most CharGen tables in Mercenary are not Imperial services (even the very existence of an Imperial Army has been questioned in the same board), but probably local ones, be them planetary or national in balkanized planets.
Even for the Marines, if it was only about Imperial Marines then there will not be the +1 in MOS table for TL 12+, as all of them would be TL 15.
Fair enough, although I'm firmly in the camp of "there is an Imperial Army" although there are many ways it might be implemented. Seeing as its an In the OTU thread I thought it best to take the top down view of how "the Imperium" would approach each assignment type. The Zhos, the Sword Worlders, Solimani and all the local, planetary level and below, militaries would face slightly different opponents and circumstances.
I think we can paint some broad brush strokes at what LBB4 means by each assignment, but its up to the Ref and the Player to really flesh out how that assignment was experienced by the character. Here's my take:
Raid
You were part of a strike into enemy held territory. The objective was to get in and out and accomplish whatever your commander's aims were, it was not to take or occupy enemy territory. The objective of your raid may have been to destroy a specific target, to take prisoners or steal supplies, you may have been probing the enemy defenses for intelligence or purely harassing him. Surprise and speed were key.
Counter Insurgency
The locals were making trouble and you were sent to combat them. Intelligence and light infantry skills were most important in finding and engaging the enemy. As well as going out and fighting the enemy combatants part of the job was winning hearts and minds of the population. You tracked the enemy down, cleared him out of areas, assisted with the rebuilding then provided security as the administration re-established control. It was a strange assignment never quite knowing who the enemy were or where they might strike next.
Police Action
You were involved in a short sharp military action designed to impose the will of your government on the enemy. It wasn't a war, because nobody could challenge your government, and they don't get involved in wars that are long and costly, but there was a lot of combat. When you were finished the enemy administration had come around to your way of thinking, or had been replaced.
Garrison
People say garrison duty is boring, but most garrison are located near training areas where skills can be honed and training exercises conducted. When you're not training your cleaning or drilling or doing the job the garrison was sited there for; keeping an eye on the locals. You have to be ready to be called out at a moments notice, whether thats being mobilized for war, deployed for limited combat operations or providing aid to the civil power in disaster and emergency situations.
Internal Security
You were sent somewhere dangerous, where part of the population had to be watched and guarded against. There was a lot of patrolling, first to show your presence, reassure the good people and discourage the bad, second to obtain intelligence. You observed everything, out on patrol or setting up an OP to watch the movements of suspected enemy. If you had technical skills you may have gathered signals intelligence listening into enemy communications. You guarded things too, things the enemy wanted to get to. That meant more patrols and roadblocks and security checkpoints. When things went wrong you were part of a quick reaction force, dispatched to deal with the trouble.
Ships Troops
You were assigned aboard ship as a deployable combat element of the ship's company. The crew actually operated the ship but you had plenty of other responsibilities when not deployed. Security within the ship, posting guards on vital areas, acting as ship's police, reacting to boarders if they made it on board. You might be deployed away from your ship for short or extended periods but your ship was always your home and your base. Combat operations and landings were what you expected but there were also humanitarian missions and show the flag events where you had to do the whole dog and pony show.
You know what's missing from that list;
All Out War.