Anyone have any good tactics with the Orca other than stand and deliver? These things are priority targets and can take alot of killing, but I recently had to fight off two scorpions popping up and attacking in the rear. The orca survived but they disabled the weapons systems before he could squash one with a stomp attach and supporting heavy infantry killed the other. I ended up only getting one turn of shooting out of him once he moved up and the driver took over the weapons.

For your first tactic, I suggest you turn in around and face the rear towards your enemy and just park it like that. Other than that, you can try not taking it. I think that's a good idea.

The Orca is an absolute BEAST. It held up to two scorpions up the rear, and took SP vs SP. Once I took out the weapons, well, it just moved points over. I am in fear of it. It will always be my first priority to kill.

Oh, if is there a self destruct button, I would offer that as a third tactic.

I play mishima and walkers are a main target for my Tiger Dragons. They are perfect for the job. Cheap, great AVV, can RD at the rear of a walker. If they do not kill it they block it for few turns until more infanty arrives on foot. I play to use 3x3 in a 750 games. My advise is to use light infantry to protect Orcas from scorpions, tiger dragons etc. Orca is made for shooting so move and shoot. It is slow, but remember that You can move 3x4"+6" to change a fighting position.

Orca is expensive and there are many cheap units that can block it. That gives an emeny point adventage. Try to avoid it.

Scorpions are bad news one way or another when it comes to Vehicles. Their main job is to hit hard on their first turn and then die. I think the only way you can avoid this to any degree is by using a old World War 2 tactic - protect your tank with infantry. It might behoove you to use the cheapest vanilla squad of Light infantry and form a shield around your rear with them. Set them to Sentry so they can at least get a few shots off at the Scorpions. Yes it is extra points but you need to consider what is more important in a game - 55pts of troop (which give you a resource!) or 165 tank.

Also keep in mind he is using 190pts to take out a 165 target, frankly it is a loss for him.

I typically protect my Orca and backfield with my heavy infantry.

Just like he said above protecting your vehicles with a layer of troops is very useful.
It might hinder movement a bit, but I usually get my heavies into position to cover everything. I don't take light infantry as they just don't hit hard enough nor are they particularly good at CC. Heavies are both. Those chainripper bayonets make cleaning off melee units from the Orca's heels less of a hassle. So does the Falloway slam.

On rare occasions when my center line is solid (and not in chaos), I will send my orca out on a flank or on its own seek and destroy mission.

I seem to always pick the multi rocket launcher for TTB:1 to increase the RoF. As in most occasions it has the best area coverage. But this is highly situational, though the pull is there every time I activate the dude.

Against a melee centric army I would use the orca as my center and screen him with my heavies. If the screen gets broken then they still have another round of shooting to deal with from the orca.

Against a ranged army there's not much to be done but try to find some cover and keep them at the edge of the 30inch range band for as long as you can. The orca is not a vehicle killer. He seems to me to be very anti infantry.

Against heavy rd army the orca is not a very good option, but can weather an attack nicely if there is minimal avv. If not then kiss it goodbye.

So to recap. It's a troop killer used to clear massed troops, take potshots at solos with the hmg, and solo/squad leader hunt with the crit force 2 auto cannon. Keep him away from melee or screen him well. Especially weak against crucifiers...