Deploy these guys wherever you like to win command struggles, then send them all to help Ragnar.  Great unit!

Or, snipe a Command Struggle with Ragnar, and when opposing Warlord turns up, move as many as you need to in order to win that struggle. Or send Ragnar to a planet with no enemy units at it, move the Sentinel to take command there, then use Blackmane's Hunt to move your warlord to wherever he is needed to win command on his own.

Main selling point here though is that a 2 cost signature squad card fills a nice space for Space Marines, who tend to struggle to  play decent cheap command cappers.

Also, of course, its drop poddable, though not optimised for that role.

The only problem I see with this unit is that if he is at planet to edge your opponent out for a command struggle, unless you put you send your general to that planet he is pulled out and you may lose the command struggle at that planet.

It's not a Forced Reaction so, as I understand it, you wouldn't *have* to pull the Sentinel away from a command struggle (or other battle) at all.

I also see this unit as a perfect target for blackmaines weapon. I dont much like the +2 option on a warlord but on his sig unit it makes more sense. 

First Space Marine Army with an Mobile-like ability, in fact this could be considerd to be super-Mobile.

Because of it's ability and possible allience with Tau (and Ion Rifles) this card gets a 4/5 for me.

If these guys are in your HQ and you use their reaction can you commit them to the same planet as your Warlord and not have them be exhausted like the rest of your cards that commit from the HQ?

If these guys are in your HQ and you use their reaction can you commit them to the same planet as your Warlord and not have them be exhausted like the rest of your cards that commit from the HQ?

No, because they will have already committed to the planet with your Warlord and been exhausted as a result.

A little extra detail: Units move from the HQ (and exhaust) at the same time as your warlord. There is no space between committing the warlord and moving the units in which to trigger the Sentinel's reaction.

Ok, thanks guys. That makes sense. I'm really new to this game and still trying to figure out the nuances. 

I am not sure I understand, do they exaust when following the warlord from HQ?

Yes. During the command phase, all units move from the HQ at the same time, so a Sentinel in the HQ would arrive at the planet (exhausted) at the same time as the warlord. It would then be unable to use its reaction because you cannot "move" from the place you are to the place you are. 

The benefit of this unit's effect is to Deploy it at one planet, commit your warlord to a different planet, then move the unit to join your warlord.

Thank you for the clear explanation, it makes sense now

Reactions are used immediately after their triggering condition happens - so these will always me before any command struggles are resolved.