Forum adverts like this one are shown to any user who is not logged in. Join us by filling out a tiny 3 field form and you will get your own, free, dakka user account which gives a good range of benefits to you: No adverts like this in the forums anymore. Times and dates in your local timezone. Full tracking of what you have read so you can skip to your first unread post, easily see what has changed since you last logged in, and easily see what is new at a glance. Email notifications for threads you want to watch closely. Being a part of the oldest wargaming community on the net. If you are already a member then feel free to login now.

You've got the generic rule for Stratagems:

You can use the same Stratagem
multiple times during a battle, but you
cannot use the same Stratagem more than
once in the same phase.

Then you've got Rites of Battle(and differently named but similarly worded bespokes on Guilliman, Ventris, Ursula, etc):

Rites of Battle: Once per battle round, one unit from your
army with this ability can be targeted by a Stratagem for
0CP, even if another unit from your army has already been
targeted by that Stratagem this phase.

Finally you've got a bespoke escalator on Overwatch itself:

You can only use this Stratagem
once per turn.

Now the way I figure this: the Captain lets you ignore the generic rule for in the same phase - but not the once per turn escalator on Overwatch.

Maybe by a strict RAW they can all repeat in the one phase, but I don't think that's RAI.

Cae use once per turn. Captain doesn't overcome that period

Then you get the Hexmark Destroyer, who says they can use Overwatch even if someone else already used it that phase.

Rites lets you use almost all of the stratagems more than once per phase. The additional restriction on Overwatch Fire is more specific, so Rites doesn't work. It's just like previous editions where deep striking out a land raider doesn't let you assault out of deep strike--if two rules say you can't do something, you need to address both of them.

Compare:
Rites of Battle: Once per battle round, one unit from your army with this ability can be targeted by a Stratagem for 0CP, even if another unit from your army has already been targeted by that Stratagem this phase.

Pouncing Hunters: You can target this unit with the Heroic Intervention Stratagem for 0CP, and can do so even if
you have already used that Stratagem on a different unit this phase.

That's language addressing the "once per phase" rule, not a "once per turn" rule.

I think the intent with 'once per turn' restriction on Overwatch instead of 'once per phase' is so that can't Overwatch against the same unit twice a turn (once in the Move phase, again in the Charge phase).

Less clear is the intended interaction between Overwtach's 'once per turn' and Rites of Battle, et al.

Prime candidate for an FAQ.

 AduroT wrote:
Then you get the Hexmark Destroyer, who says they can use Overwatch even if someone else already used it that phase.

And this seems to be the answer to the argument.
Hexmark says, "Once per turn, one unit from your army with this ability can be targeted with the Fire Overwatch Stratagem for 0CP, even if you have already used that Stratagem on a different unit this phase."

The explicit permission to use the strat multiple times per phase overrides the explicit restriction that OW can only be used once per turn.

An explicit permission overrides an explicit restriction.

You’ve got express permission to use a Strat even if used, so fill your boots.

 Elric Greywolf wrote:

 AduroT wrote:
Then you get the Hexmark Destroyer, who says they can use Overwatch even if someone else already used it that phase.

And this seems to be the answer to the argument.
Hexmark says, "Once per turn, one unit from your army with this ability can be targeted with the Fire Overwatch Stratagem for 0CP, even if you have already used that Stratagem on a different unit this phase."

The explicit permission to use the strat multiple times per phase overrides the explicit restriction that OW can only be used once per turn.

An explicit permission overrides an explicit restriction.

No. That is only applicable to the Hexmark because it gives explicit permission for units with the Inescapable Death rule. Notice how it is so powerful that GW only allowed one unit with the rule to use it per turn?

Now GW may be fine with it, but currently the Rules Commentary does not have any guidance over this type of rules priority.

 JohnnyHell wrote:
You’ve got express permission to use a Strat even if used, so fill your boots.

That overcomes one restriction, but not the more specific restriction on overwatch. This contrasts well with the hex mark ability.

The issue with the Hexmark is it also says you can use Overwatch even if someone else used it in the same phase, using the same words as the generic any strat version, and also makes no mention of canceling the once per turn rule on it.

nosferatu1001 wrote:

 JohnnyHell wrote:
You’ve got express permission to use a Strat even if used, so fill your boots.

That overcomes one restriction, but not the more specific restriction on overwatch. This contrasts well with the hex mark ability.

IMHO this is the right, and general, answer: specific restrictions need a specific exemption to be overcome.