Is the +1 to hit a enemy unit being marked cumulative if the unit has been marked by multiple friendly units?

Example: Jim Bob's Marine Predator Squad has 3 units of pathfinders within 30cm, so Billy Ray unleashes Hell with his Skyray unit 75cm away, needing AT3+ to hit instead of AT6+

Nope

The target gets "lit" once regardless of ML numbers. Essentially after the first ML lights up the enemy, all friendlies get +1 to hit it.

Heh.

Hammerheads sustained fire on a lit target hitting at 2+ not good enough for ya?

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Let there be code.

That's what I figured, but I was hoping maybe I was wrong. Thanks for the feedback!

Oh and Parintachin, why go for 2+ when I could get a negative...just say, "Hey man, your unit is hit because I SAID so!" BAM!

Fair (o:

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Let there be code.

Probably a silly question, but presumably Guided Missiles also benefit from the +1 from Markerlights? So whilst they're technically all 6+, if ever you were in a position to fire them they would be 5+?

The "2+ to hit" in 40K elevates them above the traditional S8 missile launcher being represented by a 6+?

Yep. All Tau units firing benefit from the +1 if the target is lit. Guided Missiles actually require a ML on the target to be able to fire. The +1 isn't built into the GM to hit roll otherwise there might be confusion.