Terran gameplay (StarCraft)

Gameplay attributes

 * Average cost
 * Average power
 * Very high adaptability: only race without location restrictions (can "lift off" and redeploy most of their structures without restriction)
 * Moderately efficient building method
 * Forces are comparatively weak unless set up initially before a battle (In order to fight zerg or protoss effectively, it is essential to stim the infantry, put tanks in siege mode, construct missile turrets and bunkers, lay spider mines, etc.)
 * The SCV unit (the basic worker) can repair buildings and mechanical units faster than the other two races can regenerate their buildings' HP. The medic (only in the StarCraft: Brood War expansion) can heal the biological units and the SCV faster than the other two races can regenerate their units' HP. On the other hand, neither their units nor buildings heal themselves and their buildings will also burn (decrease HP at one per second) when they reach critical HP (red HP bar). After reaching 0, they are destroyed.
 * Due to the increased micro requirements, players usually achieve higher "actions per minute" (or APM) playing terran than the other two races.

Notable abilities

 * EMP Shockwave — Science vessel ability; it drains the energy from everything within the shock radius and, on protoss units and buildings, drains shields. This makes the Science Vessel extremely effective against protoss units, especially those like the archons who have a large number of shield points but few hit points. It also has the useful ability to destroy protoss hallucinations.
 * Nuclear Strike — Requires a nuclear missile to be built in a nuclear silo (add-on to command center); then a ghost can spot a target for the nuke by pinpointing a red dot on screen. Note that all players will be notified that a nuke is being launched. After a short time the missile lands, doing massive damage to all nearby units and buildings. A nuke will deal either 2/3 or 500 damage to the target, whichever is greater. Anything that is not under the laser point will be dealt reduced splash damage. If the ghost does not flee after launching, it will be killed unless it has the ocular implants upgrade, which increases the sight radius of the ghost, thus keeping it out of harm's way. While the ghost is pointing, it can't move, attack or cast other abilites; however, it can remain cloaked if it was cloaked before the nuke was launched. Killing the ghost during the pointing phase of the nuke (after the screen has indicated the nuke launch and before the red dot disappears) cancels the launched nuke, which is then lost.
 * Yamato Cannon — The battlecruiser's only ability; it uses 150 energy to charge up and shoot an energy blast that has a range of 10, one of the longest ranges in the game. The blast does 260 damage. However, the range of the blast is longer than the sight range of the battlecruiser, so scout the target before firing for maximum range. Also, if the targeted unit is destroyed, the cannon does not fire, and the energy used to fire is lost if the cannon was already in the process of firing.
 * Heal — Medics are relatively low-tech units that cost only 50 minerals and 25 gas but are extremely effective when combined with other infantry. Terran players often use a marines and medics combination in the early game versus zerg players.

Infantry

 * SCV (space construction vehicle) &mdash; Worker. The SCV is considered to be both biological and mechanical. As such, it can be either repaired by another SCV or healed by a medic; it is also vulnerable to a ghost's Lockdown and a queen's Spawn Broodling. Compared to the other harvester units, the SCV has the most hitpoints.
 * Marine &mdash; Basic attack unit that can attack both land and air units.. They are also the only "first-tier" unit that can attack air targets. It is vulnerable to reavers and siege tanks.
 * Firebat &mdash; Attacks only ground units, it has a short-ranged attack that does splash damage. Splash does not hurt your own units, but will damage allied and enemy units. Firebats are very specialized units. They annihilate small-sized melee units (zerglings, other infantry), but later in the game, once the opponent has more ranged/air units, firebats become less useful. Requires academy.
 * Medic (StarCraft: Brood War only) &mdash; The medic's main purpose is to heal biological ground units. Apart from its basic "heal" ability, the Optical Flare and Restoration abilities can also be researched. Optical Flare "blinds" its target, reducing its sight range to one and removing any detection abilities. Optical Flare can only be removed by other medics using the Restoration ability. Restoration is a handy ability that allows the player to remove the effects of an enemy's special abilities from a single unit (except for the protoss stasis field). The medic also heals allied units. Requires academy.
 * Ghost &mdash; The ghost has several special abilities. It can engage a cloaking device (draining additional energy as it stays cloaked) and "Lockdown" enemy mechanical units, immobilizing and disabling them for a short period of time. Their most devastating ability is the targeting of a specific point for a nuclear strike. The ghost is generally used for its special abilities rather than combat prowess. Requires covert ops add-on and academy.

Mechanical units

 * Goliath &mdash; Mech assault unit, attacks air and land units. Goliaths are exceptional when coupled with siege tanks and marines, and are essential for base defense, especially against zerg (as they are mobile and, with the range upgrade, can attack guardians at maximum range, unlike the stationary missile turrets). They are, however, large in size and tend to be clumsy when ordered to walk in large groups. It is weak to swarms of zerglings and zealots and less effective against heavy units. Requires armory.
 * Siege Tank &mdash; Can change from Tank mode to Siege Mode (once it is researched), making it a stationary long range heavy artillery piece, and back to Tank mode again to move. During transformation phase and in siege mode, the siege tank cannot move or attack. A tank in siege mode has the longest attack range of any unit, capable of shooting farther than it can actually see, so efficient scouting is essential. However, while in siege mode the tank cannot attack targets at melee range, rendering it vulnerable to any massed close-range unit. In siege mode it inflicts splash damage. These features make it both an crushing siege weapon and a withering defensive unit. In combat it requires much support against melee and air units. Requires machine shop add-on.
 * Vulture &mdash; This terran hoverbike is best known for its ability to deploy spider mines, as well as for its great speed. With the speed upgrade it is the fastest unit. Vultures are excellent scouts and skirmishers, and are highly effective against protoss zealots, especially with support. However, due to their concussive damage, they are ineffective when used alone against large units. Their attacks do great damage to protoss shields (which take full damage from all attacks, regardless of damage type). Their grenade launchers cannot target air units.
 * The spider mine (when idle) mimics the zerg burrowing capability. If an enemy ground unit wanders too close, the mine pops up, approaches its target and detonates, dealing direct and splash damage. Spider mines can be destroyed either while they are tracking their target, or by other units with the help of a detector. Spider mines themselves are not detectors, but they will still target cloaked units, making them useful against dark templar. Spider mines are not activated by flying or hovering units, such as the High Templar, but will deal damage to hovering units in their blast radius.

Air

 * Valkyrie (Brood War only) &mdash; This heavily armored flying attack frigate utilizes an extensive supply of air-to-air missiles that, individually, do light damage, but have a large area of effect. They are extremely effective against air support units such as mutalisks, scourge, or tightly-grouped overlords, guardians, scouts and Wraiths but are mostly ineffective against heavier air units. The Valkyrie was added to the expansion mainly to compensate for the terrans' weakness to the zerg mutalisk rush. Requires armory.
 * Wraith &mdash; Starfighter produced at the starport, can be upgraded at the control tower. Once the cloaking ability is researched, it can become invisible for a period of time. The wraith is good for hit-and-run attacks on enemy workers, escorting larger ships, and engaging enemy air units. It is fairly effective in groups against other air units but does little damage against ground units and buildings.
 * Battlecruiser &mdash; Arguably the most powerful terran unit in the game, it can be outfitted with the Yamato Cannon (a magnetically-focused nuclear blast that must be researched), and can attack air and land units. However, its normal laser attack has an extremely slow firing rate, and battlecruisers with no support are vulnerable to masses of zerg scourge and devourers (in Brood War), or groups of scouts, and even wraiths. Though the Yamato Cannon consumes a great deal of energy, the tremendous beam of energy can obliterate many small units or buildings in one hit, such as the protoss photon cannon. An upgrade of the storage capacity for energy points is available. Production of the battlecruiser takes place at the starport and requires a science facility with the physics lab add-on.
 * Science Vessel &mdash; Spellcaster, no attack. It can detect cloaked enemy units in its vicinity; can place a "defensive grid matrix" around other units, including other science vessels, but not itself, which functions as an extra shield for a limited time; or can fire an EMP shockwave to drain all buildings and units of shields and energy that are within its blast radius; can "irradiate" an organic unit, causing it to slowly lose hit points until it dies or takes 250 damage (whichever comes first) &mdash; this also damages other nearby organic units. Requires science facility.
 * Dropship &mdash; Flying transport, no attack. It is slightly faster than a protoss shuttle that does not have the Gravitic Drive upgrade, but much slower than one with. It is also faster than upgraded overlords, and its toughness lies between them and the more fragile shuttles. Requires control tower add-on.

Basic buildings
Unlike the buildings of other races, the major terran buildings are mobile; they can lift off, fly slowly, and land elsewhere. Only air-to-air or ground-to-air attacks can damage these buildings when in the air. Buildings that have been lifted off can be repaired in mid-air by SCVs. If the building has an add-on, the add-on is left behind (and can be claimed by any player who lands the appropriate building next to it). Add-ons (which are unique to this race) can only function when the main building is attached, and any one building may only have one add-on attached. Unlike other races, a terran building will burn down (take damage automatically) if its hit points reach critical (red HP bar, less than 1/3 of total hit points). Hit points slowly decrease until they reach 0, when the building is destroyed and must be rebuilt. Only SCVs can prevent the building from burning down by repairing the building into the yellow or green state (greater than 1/3 or 2/3 of total hit points, respectively).

Terran buildings are also bulky and have a tendency to take up a lot of space, filling up bases quickly. This is mostly because supply depots, unlike protoss pylons and zerg overlords (technically not buildings but still supply), serve no other tactical purpose within the game. However, they can be used as "walls" to force enemy troops to walk a longer way around or slow down their "rush" to attack the buildings first.


 * Command Center &mdash; Trains SCVs and serves as a drop-off point for resources. Also contributes 10 to the supply.
 * ComSat Station add-on &mdash; Scans a spot on the map for several seconds, using energy. Reveals all enemy units (including cloaked or burrowed) and buildings. It is an efficient and risk-free way of scouting out an enemy base (requires academy).
 * Nuclear Silo add-on &mdash; Produces and launches nuclear missiles (requires a covert ops add-on for the science facility; requires a ghost to launch).
 * Supply Depot &mdash; Contributes 8 to the supply limit, with a maximum of 200. As they are needed for supply, they are constructed in great numbers. However, unlike zerg overlords (which are air units and take up no space) and protoss pylons (which are also needed for powering structures), supply depots serve no other inherent purpose, and take up the most space of any main supply-providing building/unit.
 * Engineering Bay &mdash; Provides upgrades for armor and weapons upgrades for infantry. Requires command center.
 * Barracks &mdash; Trains marines, firebats, ghosts, and (in Brood War) medics. Requires command center.
 * Refinery &mdash; Allows the harvesting of vespene gas from a geyser by SCVs. The SCV which builds the refinery will automatically start harvesting from it.
 * Missile Turret &mdash; Provides automated surface-to-air attack (though manually targetable) and includes detection capabilities. Requires engineering bay.
 * Academy &mdash; Provides special ability upgrades for infantry and the ability to train firebats and medics (upgrades include Stim Packs for marines and firebats, U-238 shells for marines, Restoration, Optical Flare, and energy upgrade for medics). Requires barracks.
 * Bunker &mdash; Has no attack of its own, but can house up to four infantry (marine, firebat, ghost, medic, or SCV). Units inside sustain no damage, and are free to return fire. They also receive a slight range increase, that, marines combined with U-238 Shells, puts them on equal range footing with upgraded protoss dragoons. If the bunker is destroyed, all units inside survive the destruction unharmed and appear in the "ruins" of the bunker. Units inside the bunker cannot use special abilities (such as healing or targetting a nuclear strike). Requires barracks.

Advanced buildings

 * Factory &mdash; Constructs vultures, siege tanks, and Goliaths. Requires barracks.
 * Machine Shop add-on &mdash; Provides upgrades for mechanized ground units (spider mines and speed upgrade for vulture, siege mode for tanks, and the Goliath air range upgrade in Brood War only).
 * Armory &mdash; Provides weapon and armor upgrades for factory and starport units and is also required for Goliaths and Valkyries. Requires factory.
 * Starport &mdash; Constructs wraiths, dropships, battlecruisers, science vessels, and Valkyries. Requires factory.
 * Control Tower add-on &mdash; Allows for upgrades to the wraith (cloaking ability and energy upgrade).
 * Science Facility &mdash; Allows for the construction of and upgrades to terran science vessels (EMP shockwave, irradiate, and energy upgrade) (also required for second and third level armor and weapons upgrades at engineering bay and armory). Requires starport.
 * Physics Lab add-on &mdash; Allows production of battlecruisers and provides upgrades for them (Yamato Cannon and energy upgrade).
 * Covert Ops add-on &mdash; Allows production of and provides upgrades for ghosts (sight upgrade, Lockdown, cloaking, and energy upgrade).

Techs
Terran players usually follow one of two main general tech trees: 1) Biological (infantry) and 2) Mechanical (metal). It is not good to mix and match (unless engaged in a long match) because many buildings (such as academy/engineering bay and armory) upgrades for only one of the two tech trees.

1) Biological is often used against zerg opponents because of just how effective marine/medic is against almost all zerg units (with the exception of lurkers). It is not as effective against protoss or terran units because these races have more larger-damage units, with splash.

Against zerg opponents, a typical build order would be a couple of barracks and supply depots (can also implement building block - see Strategies), refinery, academy, more barracks, ComSat, factory, engineering bays, starport, science facility, and then expand to more buildings as you see fit. Generally, terrans cajust pump out Marine+Medic, some tanks for siege support, ComSat for detection, and science vessels for detection and irradiate.

2) Mechanical is almost always used against protoss and other terrans because infantry is often ineffective. The mechanic units include tanks, vultures, Goliaths, and maybe wraiths and battlecruisers.

Against protoss and terran opponents, a typical build order would be a supply depot + barracks building block (see Strategies), factory (2), starport. From then on, the terran will have to choose which specific strategy to implement, depending on various circumstances.

Strategies
Here is a list of some simple and common terran strategies:

Wall-in &mdash; This strategy is also called "turtling." On certain maps (Lost Temple, for example) there are positions where one can build a supply depot and barracks where the two buildings can block units from entering or leaving. The barracks can be used as a portcullis, as it can be lifted to allow units to pass underneath. This allows the terran to defend their block from within the base (although this has rarely also been used offensively) with ranged units such as tanks and marines. This is extremely effective because the block are actual buildings and can be quickly repaired by SCVs if under attack, similar to repairing a wall from where one can mow down the enemy forces with barely any casualties. This is often used in the early stages of the game, where terrans would generally tech up to metal units and would need a reliable wall to stop enemy forces from ravaging the base until reinforcements can come.

Dropping &mdash; One of the most notorious attacks terrans are known for. After teching to starport and getting dropships, terrans can drop units by loading them into dropships and dropping them near weaknesses in the enemy base, causing large amounts of damage. For example, terrans often drop siege tanks onto cliffs overlooking the enemy base and immediately siege them, attacking their buildings and units. Because the tanks are on high ground, the enemy cannot easily fend off the attack. Drops can also be tactically used to destroy the enemy resource gatherers (using fast-attacking concussive/normal damage type units such as vultures and marines) and delay their economy for quite a while. And finally, drops can also be used as a large-scale attack force. Sending a group of 6-8 dropships and a science vessel or two, terrans can unload a whole army of tanks, Goliaths, and marines+medics inside an unguarded point in the enemy base.

Wraiths &mdash; Wraiths are often used against enemy terrans, due to their lack of ready detectors. With their Cloaking ability, wraiths can attack targets unguarded by stationary turrets or science vessels. Even with a ComSat scanner, detection is only temporary; the wraiths can retreat, and attack again. In addition, a wraith rush can be somewhat effective against zerg players in hunting down overlords and slowing down their army. Wraiths are also very good for harassing.

Irradiate &mdash; Used primarily against zerg opponents, or expensive protoss units such as a high templar or dark templar. A variant strategy involves irradiating one's own mechanical unit (such as another Science Vessel), and moving it into melee range with enemy units, particularly workers, damaging and killing as many as possible before the Irradiate wears off.

Tank Push &mdash; This refers to the practice of "leapfrogging" siege tanks into enemy positions. Since the range of sieged tanks is so large, one can attack the enemy base and destroy its frontline defenses, then inch some tanks forward and continue destroying the defenses behind those.

Bunker Hopping &mdash; Refers to the similar practice of "leapfrogging" bunkers. One bunker staffed with marines is used to defend the SCV building another bunker which is then staffed to protect the building of another bunker, et cetera, to create defense in depth.

Good Bunker Defense- One common mistake that amateurs make is randomly placing their bunkers, Goliaths and siege tanks, creating a divided defense system. The proper placement of defenses is to have bunkers in front that are being repaired by SCVs, followed by Goliaths or missile turrets, and finally siege tanks at the rear. This strategy is most effective when it is used in the vital choke points of your base, reducing the effectiveness of swarm assaults by terran or zerg opponents.

Against the Zerg
It is important to remember one key philosophy in Terran vs Zerg (TvZ): Don't let the infestation spread. Terrans have the advantage in the early and especially in the mid game and they have to use it. Advanced hive tech allows the zerg to easily match terran late-game strength. If zerg are allowed to survive with a functioning economy into the late game, a terran base will be overwhelmed with hordes of upgraded units, and any defensive line, no matter how massive, will eventually be broken.

Early Game is classically a split between the popular fast expansion("fe") and a direct strike on the zerg main base. The decision is typically settled by the opening scout (most professionals will send an SCV to scout their opponent between 8/10 and 10/10 population). The scout will reveal if there is any opportunity to perform a marine rush on the zerg base. The rush requires immediate construction and research of academy technology, specifically medics and stim packs. Grouped correctly and with sufficient numbers, a small early-game force of marines and medics can often beat the first few defensive zerglings with minimal casualties.
 * Medics should be prevalent enough to allow for regular stim use without any concern for the medic's energy level, as this gives a terran player double the firepower from his marines.

Mid Game The balance can quickly shift against an unwary terran player when the zerg acquire lair tech. The best way to spot this is through frequent ComSat checks, though most competent players can be expected to pursue this line very quickly, as a force of zerglings and hydralisks can overwhelm defensive marines and medics for relatively low cost. Fortunately, sufficient zerg forces to defeat marines and medics require sizable quantities of gas, so if a terran can keep casualties to a minimum, the zerg player's economy will be repurposed to create more units (an opposition a reasonably competent terran player could defeat) as opposed to advancing up the tech tree (a much harder foe to conquer).
 * If you spot a zerg player constructing a lair, you should construct an engineering bay at once if you have not already. Most zerg lair tech is best handled in part with missile turrets.
 * Mutalisks are very threatening because of their speed, the second fastest in the game. Zerg players typically attempt to bottle up terran opponents by threatening their main with fierce hit-and-run micro.
 * Terrans who see the spire go up should immediately turret their resource line, barracks, and base, as spread out static defenses minimalize ricochet damage and ensure total coverage of the base. You will have to support your turrets with M&M's or the turrets will get overwhelmed, but turrets will drastically slow down mutalisk strikes and soak a lot of damage for their cost compared with 40hp marines.  While Turrets will hold back mutalisks Science Vessel are the best way to end them.  Irradiate(range 9) has a nasty habit of inflicting excessive damage on tightly grouped mutalisks, and no one really cares about loosely grouped mutalisks.
 * The potential, though unlikely, progression from mutalisks is Guardians, and Science Vessels will be a complete deterrent from this as a single irradiate practically now pays for each science vessel you build.

It should be noted that Mutalisks tend to be ignored if a base harass is thwarted, as mutalisks have little value on the defensive. Because of this average players may pursue lurkers to keep up the contain if their mutalisks are stopped not having the Hive tech for more aggressive answers to Infantry. Please note that a Potent Zerg player will not have this problem, as Hive tech comes quickly when they know how badly it's needed.


 * Lurkers are one of the few Zerg units endowed with splash, and thus the only other effective counter to mass infantry at Lair tech. One of the bonuses of getting the Engineering bay up is Infantry Armor Level 1 which makes Marines 3 hit kills to lurkers(and 5 hit kills to mutalisks, plus reductions on ricochet).  The other bonus, is being able to get cheap permanent detection on the map, which later helps ward off lurker drops.
 * If you believe that your opponent is going Lurkers your top priority should be producing science vessels, as the irradiates will quickly pay for construction, as will the map control from being able to save comsat scans.
 * Siege Tanks are an important sub set, as they will give you the range to attack the now exposed Lurkers with ease, but they should not be overemphasized, tanks are easy targets for Zerglings, a gas free counter, science vessels on the other hand will continue with irradiation effects while requiring gas intensive counters to be handled. In other words, there are better things to put gas into than tanks, specifically, Science Vessels and Dropships.
 * The goal of tanks is to attrition lurkers, not necessarily to obliterate them. If you can force them to move you can win the battle because of the myriad options a mid game terran player has against lurkers.
 * ~ M&M's can micro very effectively against Lurkers, and will frequently drain a great deal of gas from a zerg player who doesn't support his Lurkers with zerglings. You need to stim whenever you expect the lurkers to unburrow, particularly when you begin to siege your tanks in front of them, this way if they try to up and run your marines will be faster.
 * ~ Dropships are just as Vital as marines, and a well placed drop can encircle the lurkers, either cutting them off from reinforcements or more likely retreat, this is risky without knowledge of much of the map however, as rines placed directly behind front lines can be just as easily encircled if your opponent sees what you're doing and keeps his lurkers in the ground. What's better is for you to find your opponent's tertiary or quaternary expansion for a drop.  A good player will send a lurker or two to defend completed hatcheries, but if he's pushing your front he might forget, or simply prefer to use all of his available lurkers to occupy your marines in the hopes that you might forget how critical a successful drop can be at this phase in the game.  No matter what being able drop will pull lurkers off his front and likely distract him long enough to force a speedy withdraw from battle, rather than the micro intensive slow one that will allow him to freely pursue Hive Tech.

Hopefully you will have noticed that every zerg tactic mentioned above is essentially a stall tactic, that is both because of the dominant position terrans have at this point in the game, and because of the untold horror which the Zerg can unleash against the Terran:

Hive Tech: Marines are crucial to Zerg, they cost no gas, and yet there is little a zerg player can do to fight them that doesn't seem to cost a great deal of gas. As great as it may seem, the zerg have some tricks left that will even the odds in every late game scenario where the terran player does not have a dominant position on the map.

We'll start with the least micro intensive tactic that everyone can use with maniacal joy; Ultralisks. This unit is the antithesis of a Zerg unit; everything that a zerg unit is the Ultralisk is not. It is not small, it does not have low hit points, it does not need to be massed, it does not burrow, it has a low attack strength, though it does have a bit of speed for a 400 hit point mastodon of bloody fury. The upgrades Brood War expansion render these obvious monsters a total affront to any god a terran has bowed before. I complain but the terrans have the medic and Charon Boosters, and that's not too bad. So, your opponent is building Ultralisks, what now?
 * Keep Building Marines. It sounds hopeless when your marines are only doing 3 damage a shot to 400 hit points, but they didn't cost you any gas, which makes them great filler.  They also are important for killing whatever else the Zerg player builds to support the ultralisks.  Typically this support is composed of zerglings, as they cost no gas, which are best handled by your marines.  There's also the fact that Ultralisks have a fairly low damage rate, so most of the losses players see when Ultralisks are deployed don't come from the Ultras at all, which means they will never be the only thing you have to deal with.
 * Cast Defense Matrix(DM) on your front line Marines. If you've got the fingers for it this works great, suddenly a 200 mineral 200 gas 400 hit point giant doesn't seem so menacing when you can make 290 hp foot soldiers for 50 minerals and 100 energy.  This is a really good reason to have Science Vessels in your late game.
 * Irradiate the Ultralisks before they start attacking your marines. Often you can encourage an Ultralisk attack to happen prematurely by irradiating the intended Ultralisks, they won't die, but losing 3/4 their hp is pretty close, if your opponent does attack this will likely mean that his ultralisks will also deal irradiation damage to the zerglings in the control group, and those zerglings are after all your real targets.
 * Use tanks. The obvious approach is to use the massive explosive damage of tanks to quickly bring down ultralisks, but this is contingent on your tanks actually targeting the ultras and not the supporting lings, in addition to your tanks not dealing splash damage to your own troops.  The worst part of this strategy is that should you be overcome you will have little hope of your tanks surviving point blank Ultra-ling.  Some of these problems can be fixed by using unsieged tanks which don't deal splash damage to your units, but this play is only worth while if you have excess resources given the heavy reduction of ultra armor, and the low armor of tanks(less per mineral than a marine!).  Always Defensive Matrix your Tanks before your marines.
 * Spider mines. The only time Vultures should enter into a TvZ match up.  125 splash is a good way to cut through 400 hit points, shame that Ultralisks set to Attack-Move can attack and kill a spider mine in one hit before it has a chance to detonate.  Basically this means that spider mines are only useful if the ultralisks are already chasing something else,  Which takes out a lot of their punch.  This strategy is usually seen as an act of desperation, and it is.

Defiler A competent Zerg opponent will use both Defilers and Ultras for excessive amounts of annoyance and advantage, knowing what the ultralisk is capable of, it's role is obvious, what's important here is the Defiler's role.

At 350 gas the defiler is by far the most important target to irradiate. Sadly Irradiate does not stop a defiler, it only determines a life span. Still if you can keep your science vessels aggressive and your opponent's gas low Defilers can remain a contained threat. But to maintain this situation practically requires you to destroy your opponent outright, which is highly recommended. Your best bet is to destroy your opponent's expansions, cutting his ability to field an army which could benefit from such awesome tech:
 * Dark Swarm (100 energy, or 2 zerglings)("DS") Completely Blocks all direct fire from ranged units. This leaves a terran with Tank Splash and Irradiate, which is why you should run from or past dark swarm.  Note that Splash damage does not effect burrowed units, which means that a few lurkers burrowed under a perpetual dark swarm can form a pretty effective seal on a base until you have the energy to irradiate all of them.
 * Consume (+50e, costs one unit) This is what really makes a Defiler incredible. The fact that you can buy energy for a single defiler with crystal and never have to worry about recharge rates breaks the natural rules of casters.  With this even and Irradiated Defiler can cast 2 to 3 spells and mostly be limited by how fast it can scuttle within range of targets.  For this reason above all else the Defiler should be not be allowed to enter the field of battle if it can be at all helped.
 * You may also see Plague, particularly because it's a good way to spend 3 lings when a defiler has already been irradiated, so watch out for the lone mutalisk which will come around to do one hit kills on any sci vessels affected by plague.
 * The best way to handle Defilers is to keep moving, either falling back of pushing forward. Always be ready to flank, and never hole up.  To this end Dropships and Science Vessels are the only real salvation you can hope for.

To make final what has been said
 * Pump Infantry.
 * Push your mid game offense.
 * Destroy your opponent's expansions at every chance you get.

Against the Protoss
Because Terrans have the weakest early-game detection, a popular Protoss strategy when dealing with Terran Players is to wall himself in with Photon Cannons while teching to Dark Templars. The Dark Templar Rush as its called is quite capable of causing severe damage to an early game Terran assault, for Templar can one-hit kill Marines, and slice Missile Turrets to pieces easily.

There aren't many ways to prevent this. In a map like Lost Temple, the Terran should attempt to block chokepoints with supply depots with a single Barracks being used as a "Gate" of sorts, lifting off to allow your own troops to move through, or landing to prevent enemies from advancing. Supported with two or so missile turrets, this will prove a decent defense unless the enemy decides to use a Shuttle and just fly around these defenses. Additionally, hotkeying a Comsat Station can work in a pinch; the 1-s-click as its called can temporarily nullify the Templar cloaking ability. Spider mines also work for they home in on cloaked units, and as of more recent patches, a Dark Templar has 40 Shields and 80 HP, meaning that a spider mine will kill it in a single hit while weakening any nearby Dark Templar.

The same wall-in suggestions work when fighting a Zealot Rush, for between their speed and durability, Zealots generally will just run past the Terran's base defenses and go straight for the SCVs, crippling the economy enough to win the production war that is Starcraft. Walling in works well for hindering the movement of Zealots, especially if Bunkers comprise some of the walls.

Concussive-damage units are a lot more effective against Protoss than normal, since Shields take full damage from every attack type. Firebats in particular easily beat their cost worth in Zealots as the splash-damage combined with Protoss bunching to attack units makes them very damaging. Keep a few medics around to allow more liberal use of Stimpacks; such a defense should help protect against the Protoss until one techs to Vultures.

Vultures are perhaps the best mid-game unit to use en-masse vs. Protoss. A single Vulture is cheaper than a Zealot and does more damage for the cost, and at range. 8 Vultures can take out a Zealot in a single salvo, and with proper micro can defeat many times their cost in Zealots. Versus heavier units like Dragoons, they can run up, deploy a mass of spider mines, then retreat; this tactic can easily be supplemented in the late-game once Ghosts appear, for Protoss have no counter to Lockdown. Lockdown several Dragoons and Reavers, and ride the Vultures up to drop spider mines adjacent to them. Such harassment works until Siege Tanks become available.

Against Protoss, keeping Siege Tanks in Tank Mode is a viable strategy. The Protoss units are generally durable enough to shrug off singular Siege Mode attacks that enough Zealots rushing a tank emplacement will win out; between those and Corsairs, unless the Tanks are being used for a specific purpose like shelling Photon Cannon emplacements or Reavers, they work best for hit-and-runs. They make good Dragoon hunters for such is the attack animation that a Tank shot is instantaneous and a Dragoon shot travels before hitting. Combined with a Dropship, a Terran can quickload a Tank before it takes damage, then unload it. However, this trick requires experience to pull off.

When it comes to aerial battles, Wraiths are the main unit to use against other Protoss air units for Protoss have the weakest late-game detection. True they have Observers but even Observers are vulnerable to comsat-sweeps followed by a Wraith Salvo. Unless the Protoss player uses redundant Observers, the Terran now has a window of opportunity to attack with impunity.

The Science Vessel is a powerful item for EMP works wonders on Dark Archons, Archons, High Templar, Shield Batteries, and Massed Carriers. However, other abilities are imporant as well. Defense Matrix nullifies the fragility of Vultures and a squad of Matrixed Vultures can rush past a base's defenses to go straight to Probe-hunting. However, one should beware Dark Archons with Feedback.

Battlecruisers are perfect for assault due to its damage that it inflicts on its foes but the only way to counter a full fleet of Battlecruisers is by building up as many AA units as possible and also use spells to back up.