Having just picked up a copy of Rites of Batle, I found myself quite interested in the place Kill-Marines play in the deathwatch. i know they're astartes that can function on their own and all that, skilled in bringing down the hated xenos on their own and all that. but what is their actual function? why would you send just one marine when Astartes are more or less made to function in squads? What are their other uses? and how do they interact with traditional kill teams?

I think Killmarines are used mainly to add 'muscle' to other groups, like Inquisitorial cells or Rogue Trader crews, who's interests the Deathwatch has a stake in. I don't know how you would use them in Deathwatch ; I think they were included in RoB as a way to incorperate one or two Deathwatch PCs in Ascention -level Dark Heresy .

Kill-marines are the Deathwatch marine who provides assistance to the schaffer's last chancers. They are the marines who provide escort to an inquisitor or dignitary who is meeting with xenos. They are the marines who are seconded for a specific purpose or missions multiple marines are not necessary. They are the marines you use in a Deathwatch game with only 1 player.

They could also be deployed along side a Kill Team. The kill Team could drive the quarry and the Kill Marine could just await in ambush if the Kill Team didn't take out the target. There are a number of different ways they can be employed.

Yeah, their main role is not in Deathwatch games. 40k RPG still claims all systems are crossover-compatible. That is fundamentally true, though they're not exactly crossover-friendly (the balance is literally all over the place when you mix and match games in the same team). Kill-Marines are specifically an option for when you want your Marine to roll with the Inquisition or the Rogue Traders. Any other use they may have is purely incidental.

I think they could serve alongside a kill-team, perhaps serving as a second one-man squad deployed ahead of the team. I really want to try out playing as a Raven Guard Kill-Marine silently sneaking around in power armor stealth killing people.

They are there just in case you have only one player in your group.

"One riot? One ranger."

I am aware of that, but I'm starting to think of them in more meta-game terms, since it seems like you could make one that would be utterly broken, like the previously mentioned Raven Guard (guerilla training OP), a solo-raptor sniper, frenzying Blood Angel or Flesh Tearer, it could make the game a lot more fun or interesting I think.

I'm also considering playing with just 2 people, and both of them being kill-marines could be interesting.

A Kill Marine is an Independent operator, this much we are all aware. In the entry for a Kill Marine it gives quite an elaborate number of reasons and potential story hooks as to the function and use of a Kill Marine. Missions at the behest of the watch commanders, held in secret from their brothers. Investigators, assassins, representatives of the deathwatch and sometimes the wider Imperium, diplomats (with a big frakking gun), advisers, and of course the one man army.

Kill Teams are canonized as being formed typically for singular missions, often being disbanded after completion. Sometimes these teams are together for more than one mission.

The Death Watch of my own little sector of the Imperium operate with watch captains overseeing multiple kill teams. The members are recruited for two decade long terms.

What I did was make the additional career advancements require completion training programs that each of the player characters would have to undergo in order to gain additional designations that open up more possibilities. The training programs are role play opportunities to demonstrate character development.

Why do I mention this? Because not everyone is suited to become a Kill-Marine. I found that out after only two of my players actually made it through the program. They were able to demonstrate the ability to role play a Kill-Marine to the books standards of what they are. Use of tact, wit, diplomacy, and understanding when to apply force.

So these two have earned the right to role play on their own personal missions. Which as a GM I got a slightly bigger workload with them now. In game fluff wise they have sworn an additional two decades with the Death Watch and the Watch Captain has more flexibility with deploying the characters on their own if needed trusting that they will perform the mission. We haven't had the chance yet to really get a mission on with their newly gained status due to the need of having to deploy the full kill team in repulsing a tyranid invasion...

I got few plans brewed up. If you have ever read Dan Abnetts Brothers of the Snake I drew some inspiration from the first portion of that book where a lone space marine is sent to deal with a dark eldar incursion. I thought of kinda of the same concept but with the kill marine being assigned to aid a world under threat from dark eldar raids. There would be a guard regiment stationed on the planet that could be of help. I'm still working on the missions parameters. I was also considering escalating it too and requiring the rest of the kill team to be sent in way later on. But we'll see... tryanids are kinda a higher priority...

A Kill Marine is an Independent operator, this much we are all aware. In the entry for a Kill Marine it gives quite an elaborate number of reasons and potential story hooks as to the function and use of a Kill Marine. Missions at the behest of the watch commanders, held in secret from their brothers. Investigators, assassins, representatives of the deathwatch and sometimes the wider Imperium, diplomats (with a big frakking gun), advisers, and of course the one man army.

Kill Teams are canonized as being formed typically for singular missions, often being disbanded after completion. Sometimes these teams are together for more than one mission.

The Death Watch of my own little sector of the Imperium operate with watch captains overseeing multiple kill teams. The members are recruited for two decade long terms.

What I did was make the additional career advancements require completion training programs that each of the player characters would have to undergo in order to gain additional designations that open up more possibilities. The training programs are role play opportunities to demonstrate character development.

Why do I mention this? Because not everyone is suited to become a Kill-Marine. I found that out after only two of my players actually made it through the program. They were able to demonstrate the ability to role play a Kill-Marine to the books standards of what they are. Use of tact, wit, diplomacy, and understanding when to apply force.

So these two have earned the right to role play on their own personal missions. Which as a GM I got a slightly bigger workload with them now. In game fluff wise they have sworn an additional two decades with the Death Watch and the Watch Captain has more flexibility with deploying the characters on their own if needed trusting that they will perform the mission. We haven't had the chance yet to really get a mission on with their newly gained status due to the need of having to deploy the full kill team in repulsing a tyranid invasion...

I got few plans brewed up. If you have ever read Dan Abnetts Brothers of the Snake I drew some inspiration from the first portion of that book where a lone space marine is sent to deal with a dark eldar incursion. I thought of kinda of the same concept but with the kill marine being assigned to aid a world under threat from dark eldar raids. There would be a guard regiment stationed on the planet that could be of help. I'm still working on the missions parameters. I was also considering escalating it too and requiring the rest of the kill team to be sent in way later on. But we'll see... tryanids are kinda a higher priority...

I have actually read Brothers of the Snake! Its one of my favorites and that is a perfect example. The people I am gming for are either somewhat familiar (they liked painting miniatures basically), have never played tabletop or know of the fluff, or are well-versed in the universe themselves (out of the 6 who play thats basically 2 of them).

I actually just thought of a way to incorporate one, its sort of stemming off of a mission I thought of but never drew up maps for or anything.

Basically I'm thinking of having the kill-team sent to investigate a Rogue Trader vessel that a kill-marine was stationed on as a liaison with said RT. Now the ship has kind of shown up in the reach and hasn't been responding to any attempts made to communicate with it. The team is sent in and finds the crew slaughtered and have no idea what did it (it was Rak'Ghol), they might stumble across an audio recording where some non-superstitious idiot happened to mention them by name and his disbelief in this superstition is proved wrong. The Kill-Marine, being a badass Space Marine and all is the only survivor but has been beat up a bit. Basically if they find him it'll become their priority to get him out of the ship while fending off a bunch of wall-crawling lizard alien guys.

I played a Black Templar Assault/Kill Marine in a campaign for a long time. I used the Kill Marine template because the character was like a Knight Errant. He even had his own Squire (as an experienced Tempar he had to train the grunts). He was assigned to the kill team for the same reason any Black Templar would be, there would be sorcery and demons at work. When these situations arose, my squire and I would break from the Kill Team and deploy in Black Templar solo or squad mode as needed. I'd use my Kill Marine cohesion when my squire's medical skills were needed elsewhere (he was training to be an apothicary).

There were many times i had to disengage from the Kill Team and do my own thing or take out specific targets. Blowing my own cohesion on those encounters helped the group stay out of fights they weren't tailored to that i was and save their cohesion for shredding hordes and heavy armor, which was more their forte.

I played a Black Templar Assault/Kill Marine in a campaign for a long time. I used the Kill Marine template because the character was like a Knight Errant. He even had his own Squire (as an experienced Tempar he had to train the grunts). He was assigned to the kill team for the same reason any Black Templar would be, there would be sorcery and demons at work. When these situations arose, my squire and I would break from the Kill Team and deploy in Black Templar solo or squad mode as needed. I'd use my Kill Marine cohesion when my squire's medical skills were needed elsewhere (he was training to be an apothicary).

There were many times i had to disengage from the Kill Team and do my own thing or take out specific targets. Blowing my own cohesion on those encounters helped the group stay out of fights they weren't tailored to that i was and save their cohesion for shredding hordes and heavy armor, which was more their forte.

Thats a good choice, especially being able to use your squad mode ability to get a TON of hits.

I have actually read Brothers of the Snake! Its one of my favorites and that is a perfect example. The people I am gming for are either somewhat familiar (they liked painting miniatures basically), have never played tabletop or know of the fluff, or are well-versed in the universe themselves (out of the 6 who play thats basically 2 of them).

"Because one warrior usually suffices."

Thematically, as described, they are one-man teams who operate alongide full kill-teams, or allow you to send a solo deathwatch marine to support an Inquisitor. I've considered offering a Kill-Marine to one of our group the next time we play Ascension.

Mechanically, it's also useful for a variety of reasons - firstly, some marines naturally want to be in solo mode. Space Wolves, for starters, tend to get irritable if you take Wolf Senses away from them. But most specialities have one ability which works in squad mode and one which works in solo mode and a player has to pick one or the other. If you've got a squad full of bolter mastery tactical marines, a devastator with Unrelenting Devastation may well want to be a kill-marine to allow himself to use his heavy bolter to full effect. Also, the table of skills is very, very good. Don't underestimate the value of stuff like polyglot in non "kill-everything-with-more-than-four-limbs" missions...

I played a Black Templar Assault/Kill Marine in a campaign for a long time. I used the Kill Marine template because the character was like a Knight Errant. He even had his own Squire (as an experienced Tempar he had to train the grunts). He was assigned to the kill team for the same reason any Black Templar would be, there would be sorcery and demons at work. When these situations arose, my squire and I would break from the Kill Team and deploy in Black Templar solo or squad mode as needed. I'd use my Kill Marine cohesion when my squire's medical skills were needed elsewhere (he was training to be an apothicary).

There were many times i had to disengage from the Kill Team and do my own thing or take out specific targets. Blowing my own cohesion on those encounters helped the group stay out of fights they weren't tailored to that i was and save their cohesion for shredding hordes and heavy armor, which was more their forte.

Thats a good choice, especially being able to use your squad mode ability to get a TON of hits.

That's pretty much how we did. Squire Goodwyn and I felled many a demon.