I have however spotted a nice way of combining three rules that allows marines to get a "free" 6+ cover save from AP1, AP2 and AP3 weapons. Here's how it works:
The Ultramarine combat squad is hit by the plasma cannon which scatters slightly so that it catches three marines, causing three wounds.
Power armour is no use to them, but if they use the Go To Ground rule they can get a 6+ cover save in return for giving up their movement and only firing snap shots next turn.
So the marines Go To Ground and throw one 6, reducing their casualties to two models, but still enough to force a leadership check. This is where Combat Tactics comes in. The marines can now choose to fail the leadership test, and will drop back 2d6".
|In this example the Ultramarines have fallen back 7", and are still plenty close enough to return fire on their turn.|
It's also worth pointing out that this only works when the number of wounds put on the squad is enough to force a leadership check. Of course, you could roll incredibly well and save enough models to avoid the check all together, but in that situation you'd probably be happy to pay the price of giving up movement and proper shooting for the nice healthy squad that you've got left!