Over on Warseer's Eldar Tactica, Ernest101 posted the following:
"hey guys, i am having this really big prob, i play a full mech list, when i drop my banshees, they kill almost anything i want them to kill in their path, but after that assault phase, they always get blown to bits... hardly surviving a shooting phase... any suggestion guys?"
Well, you really have three options:
1. Don't let them shoot at you.
2. Reduce the effect of their shooting at you.
3. Balance your charge so that you are still in CC during their turn.
As I see it, there's several things that can greatly influence the above situations: Fortune, Doom, Multiple Units, Screening, Cover, and Target Selection.
1. Fortune. I can't emphasize enough how useful this power is. Not only can you protect your Banshees in CC and from shooting, but you can also protect their tank as you close into range too.
2. Doom. With only a S3, Banshees often need the added boost of Doom to give them a little extra punch. But you should remember that those re-rolls are optional. Say you've get 15 hits and cause 6 wounds to a 10-man Marine squad. The immediate reaction of most people is to pick up the other 9 dice and re-roll them all at once. This will likely cause 3 more kills and No Retreat will kill off the last guy several times over. However, just re-rolling 3 means 1 more kill, 3 guys doing retalitory fire, and then No Retreat will leave just 1 guy in CC with you. Or you could just play it safe and not re-roll any of them.
An interesting thing about Doom is that the rules as written allow a re-roll no matter the first result. So you can re-roll a success just as easily as a failure. Say you just charged a 5-man Marine squad and caused 7 wounds... why not re-roll 4 successful ones? Then you'll likely only kill 4 and stay in CC with the one last guy. The trick is plausible against larger units, but trickier to predict as the stacked negatives to Ld or number of No Retreat rolls can add a lot of variables.
3. Multiple Units. Banshees have a notable habit of killing of everything in their path. One protection from this is to engage more than one unit. Creative splitting of attacks can wipe out one entire threat and minimize the return threat of the other. Example: I once charged a unit of 10 Khorne Beserkers and wrapped my assault so that two girls also hit a line of 8 Noise Marines. The Beserkers were wiped out by the other 8 girls, and the Noise Marines lost 2. Fearless hits from No Retreat took down 3 more Noise Marines and I slaughtered the rest on his turn.
4. Cover LOS. Banshees don't really care if they're assaulting in the open or in cover, at least for Initiative. Targets in cover will be slowed by difficult terrain tests, meaning they're less likely to just move out of charge range. Even better, there's also a certain psychology to terrain pieces... many players will leave a unit immobile in a "fortified position" even when it might be more tactically advantageous to back out of the position. This is especially true for pieces of cover on or right near objectives. The nice thing about taking the piece of cover from your opponent is that even if you wipe out the enemy, you'll have the benefit of the cover for yourself. Even better is if the piece of cover and/or a Consolidate move will put you out of LOS from the enemy.
5. Screening LOS. Getting Banshees to where they're needed usually means they're in a Wave Serpent. So what does that tank do after dropping them off? Though it's tempting to scream it off to some other section of the battlefield, I've found it can be quite useful to continue it in support of the Banshees. After the Banshees get out, the tank can still move and shoot. Positioning it just to the side of the unit you're going to charge can screen the Banshees from retalitory fire in a wipe out as well as leaving it conveniently nearby should the Banshees want to embark back in the next turn.
6. Target Selection. WHAT you're attacking should also be a big consideration. For example, 10 Banshees charging Doomed Plague Marines should only kill 5.56 of them.
By using all of the above is how you really maximize the output of your Howling Banshees. Because you can't charge from a moving Wave Serpent, you're having to think a turn ahead for getting them into CC. Isn't it worth it to give a little extra consideration for where they'll be after that?