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.

So my question is simple. I have been told this rule but can't find it in the book. So my example being if i have a unit of 3 obliterators and 1 has taken a wound already. I get hit with a lascannon and fail my invul save. I have to remove a unwounded model correct as the lascannon causes instant death. Or... am i mistaken and i can remove the obliterator that has taken a wound already.

You are not mistaken. An ID weapon must remove a full wound model

....from the same Wound Group

Because all the obliterators are identical in game terms, they form 1 wound group - same as if 5 identical marines are hit with a weapon they are all one wound group.