Ork Strategy Notes for combined-arms army lists.  Infantry waves work a bit differently.
General Comments:
Orks are an attrition army.  You will get chewed up crossing the board so get used to the idea, don't get discouraged and press on.  Orks are nasty once they get in close.  Being overly cautious will cause you to lose momentum.  Just don't waste troops.
Targets of Opportunity.  Orks are an attrition force (notice that's come up twice now?).  It's okay to take risks to do damage to the enemy.  It's okay to risk being out of cover or opening up holes in your battle line if it means you can take the fight to the enemy.  Swap units freely, as you have more and they become more dangerous the closer you get.  Basically, you'll want to take 2 and a half turns doing as much damage to the enemy as possible and the second half of Turn 3 worrying about objectives if you need to.
"Alleys" for infantry cover.  Try to pick deployment that provides a path of infantry cover across the board.  You want to be able to hop from cover to cover with each move, so 25-30cm apart is ideal.  Closer is necessary for the slower Gunz.
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Unit Comments
Oddboyz:  Oddboyz are a massive boost to firepower.  ANY Ork formation that intends to be shooty at any point in the game should take them.  These are one of the few things you are concerned with protecting.  Philosophies on Zzaps versus Soopaguns vary.  Personally, I prefer Zzaps for the high hit probability and TK ability.  However, Soopagunz are good for mass targets and especially when taken in pairs to take advantage of the barrage table break point at 4BP can inflict more damage against a lot of formations.
Grots:  Grots are made for assaults; think of them as expendable assault-boosters.  I used to keep them in front all the time, but nobz help remove so many BMs it's often not worth it to let the grots take the hits from long-range fire.  Grots should be close to the front so they can charge/countercharge forward during assaults, but it's probably best to keep a few boyz out front to take hits from shooting.  It can be worth it, but consider carefully whether to use them outside of assaults.
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Formation Comments
Warband: There are, imho, really 3 kinds of warbands - horde, mechanized, and supported.
From Nikki Rice on Ork Horde Warbands: Warband: These form the spine of the Ork army and fill a key role in generic ork strategy. Frequently they will have very little direct impact, don't expect your boyz mobs to take out too many units. Their chief role is to draw fire away from your more potent formations, and this is a role they excel at. Your opponent ignores your boyz mobs at his peril though, if the boyz are allowed to advance unhindered accross the battlefield and successfully engage they enemy they will cause serious damage in close combat and use their weight of numbers to rout formations in an assault. I recommend garrisoning boyz formations at the start of the game to get them a head-start at rushing the opponents positions.
A mechanized warband is surprisingly fast, much like the KoS. The wagons add considerable ranged fire and FF ability as well, making them a good double move/support assault option. Generally, the addition of wagonz turns a heavily CC-oriented formation into more of a general purpose formation. Flakwagons are a good wagon to use for firepower because the warband has 30cm range anyway and, of course, battlewagons have more transport capacity. Gunwagons rarely make a good option to mount infantry.
As far as a supported warband, that's reinforced with walkers or big gunz. Personally, I have had substantial success with a mix of Stompas, Dreads and Kans mixed in. The warband can still garrison. The boyz can get vehicular cover bonuses from the walkers if you have to get out in the open, and the walkers generally have better firepower than the boyz. Using Big Gunz for support can turn the formation into a big, tough, but less shooty version of the Gunzmob and can also be quite useful.
Stormboyz: I suggest taking them with 1-2 Deth Koptas. The mob will retain the ability to garrison (Stormboyz are scouts) and the Koptas give the formation the ability to place BMs at up to 90cm (60cm move +30cm range). They are a bit vulnerable due to being LV, but have a 4+ save.  They make an okay addition to Warbands in Landas, with their Jump Packs allowing a 15cm dismount move so the Orks can get into more CC.  Most people, however, prefer other options for Landa loads.
Kult of Speed: Fast, potentially shooty and good in assaults.  These aren't necessarily very good as line troops, but they are great for plugging holes or for flanking.  They are good for supporting a run into heavy resistance, but in a situation like that they need to be used in combination with durable formations.  The formation works best with a single dominant type of unit, i.e. almost all bikes or all buggies or all skorchas, rather than a mix.  Personally, the only unit mixing I do is adding a couple Buggies to get 30cm range for placing BMs.
They are, of course, optimal when used in multi-formation assaults.  They can double move a long way to support another formation's assault, or they can assault a fair distance to trigger an assault that another formation is set up to support.
Blitz Brigade: Take flakwagons. You have the speed to get in range most of the time, so the 15cm range difference is usually nominal. The average hits inflicted is the same and you get the AA. The consensus opinion is that the optimized Blitz Brigade is the so-called "Zzap Brigade" composed of 1 Zzap wagon, 1 Gunwagon, and 2 flakwagons. The Gunwagon is to help mitigate suppression that would otherwise go against the Zzap gun, keeping it's effective range up even after the formation takes BMs.  Some people will substitute Soopagunz for the Zzap, especially if fielding a Big or Uge Brigade, where the barrage points for the Soopagunz add up.  A minority choice is to take 1-2 Dethkoptas so as to have the better armor save in the front of the formation.
Stompas: Stompas are hard to use effectively. I'm convinced at this point that the way to take them are in a mixed formation - Stompas, Dreads and Kans. Use the cheap units to bring the unit count up for Mob Up. Lead with the Stompas. They can shrug off more fire as you close range, keeping total BM count lower, and you don't want them suppressed because they are in the back of the formation. Once you're up close enough to threaten assault the Dreads and Kanz are actually a little better for the points. If you find yourself facing MW/TK fire, you can throw the Kans out front as a sacrifice to guard the more valuable units.  Consensus opinion seems to be that unless you have a very specific purpose in mind the 3-gun option is better than the 'Ammer, especially if you mix in Dreads and Kanz which have MWCC attacks.
Big Gunz:  These units get an unfair bad rep in my opinion.  They represent decent firepower and FF for the Ork list.  They can be used as a base of fire or they can consistently double move toward the enemy, wearing them down with their large volume of fire and initiating firefights if they get close enough.  Pay special attention to having proper "alleys" of terrain as above.
The key to using them is the right choice of Extras.  Obviously, you can build them out of Big or Uge Gunzmob formations.  This allows lots of cheap gunz and access to multiple Oddboyz upgrades but they are somewhat fragile.  Add Nobz.  They will add considerably to the staying power of large Gunzmobz.  Nobz help greatly in reducing BMs, which you will need because Gunz don’t count for Mob Up bonuses.
Always add Oddboyz if possible (see above).
The second way of building a mob is by starting with the standard Warband and adding Big Gunz units as Extras.  Technically, this isn’t a "Gunzmob" but from a tactical standpoint, they function similarly.  This is more expensive, but has obvious advantages as far as making the mob much more durable.  Either approach is completely valid and you should probably choose based on your personal preferences and play style.
Landas and air assaults:  I prefer to load them with Warbands + boyz/grots. I crunched the numbers in detail long ago based on all sorts of factors, but in the end each grot is worth roughly +0.5 in an assault resolution which for an alpha-strike style formation like Ork air assault, is simply invaluable. However, other combos have their own advantages.  Many people prefer adding Nobz for the raw CC power and a few like adding Stormboyz for the 15cm dismount becuase a lot of the time you won't be able to get all the Boyz into CC.
Some prefer taking Kults of Speed (10 Warbikes for 250 points) for the extra tactical flexibility after the initial assault.  In the Speed Freeks list, the option to take 10 Outriders with the price cut for a Big formation is quite effective.  If you're in an especially Orky "leave 'em behind if they can't keep up" mood, you could take a Kult of Speed with 2 Boyz/Grotz.  Sacrifice them in the initial assault and if any survive, just drive off without them (You get BMs for the units being "killed" but, Hey!  You're an Ork!)
Don't be in a rush to assault.  Landas are great air support, especially against infantry.  Also, you want to pick your eventual air assault location carefully.  Boyz will have limited mobility once on the ground so make sure they can get someplace useful.  It's okay to spend a turn with a loaded Landa just strafing the enemy.  They are pretty tough and can take a reasonable amount of AA fire without being in grave danger.  OTOH, don't be afraid to sacrifice them (again, attrition force - 3rd mention) if you can hit a high priority or juicy target.  Just make sure it's worth it.
Fightabommas:  In larger groups these can brave flak and still hit a target.  I generally build a formation up to at least 6 before starting a second formation.  If I'm going air-heavy, I'll do a formation of 9 because it can drive through a huge amount of flak and still be nasty and a formation of 3 for activations and picking off lightly protected targets.  Due to expense, you should probably be a bit more careful with these but as with all things Ork it's sometimes worth it to sacrifice them to do damage.
Gargants: They can be very nice, especially for their wicked FF ability, which is rare for Orks, and a brutally tough "Break Their Spirit" goal.  But 650-850 points can buy a heck of a lot of other Ork units. I do field them and they do well but I only do so occasionally because my personal preference is for the horde.
As far as weapon choice, Gargants gain little by choosing Soopagunz, so go with the Zzap.  The most popular Great Gargant choice seems to be the Lifta Droppa, but taking the Twin Soopagun brings another template to the barrage so it is a viable option as well.
Ork Spacecraft: Due to a variety of factors, I don't think they will ever be viable in a tournament scenario. I pretty much consider them to be for scenario play.
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Limited time this morning, so most of this is cut/paste.  I'll do cleanup and flesh some of this out another time.  In the meantime, feel free to add comments.
_________________ Neal
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