The Battlecruiser is the powerhouse of the Terran arsenal. It is often misused and under realized.

Battlecruisers take an incredibly long time to build because of their size and power. To build a decent force of Battlecruisers, you need about 2-3 Starports constructing them. Multiple Gas Mines are necessary to make a force of Battlecruisers as well as a force of Siege Tanks, and other gas requirement units. But if you focus on Battlecruisers entirely, with Marines and Bunkers for defense, it is possible to build up a force of Battlecruisers with only one gas mine.

In small numbers Battlecruisers are easily killed. Battlecruisers need to be used in a group of about 6 or more, to start to do significant damage to the enemy on their own. Because they can only fire at one target at a time a pack of Stim packed Marines can often easily overpower a single Battlecruiser. When fighting only a few Battlecruisers you want to give them too many targets to fire on at once, such as large groups of Marines. The time required to finish off a single troop, and the delays between firing should allow you to overcome the Battleships as long as there is only a few of them with no supporting troops.

To be very effective, Battlecruisers must be built in large numbers, or be placed in a multi-type unit force to protect them. A few Battlecruisers mixed in with your Tanks and Marines will both cause fear and do some serious damage.

A Battlecruisers strength lies in its high hit points, ability to be repaired, and Yamato Cannon. By researching the Yamato cannon technology a Battlecruiser can fire a Yamato blast doing 260 hit points of damage. This can destroy most units and quickly clear out anti-air towers.

As if this large group of Battlecruisers made in a 4on4 game weren't dangerous enough, a few Science Vessels are used to use Defensive Matrix on several Battlecruisers giving them 750 hit points total a piece. (500 + 250 for the Defensive Matrix) This force was made with 3 resource spots (3 Minerals, 3 Gas), and 3 - 4 Starports. The team game battles distracted the enemy long enough for the force to be built up. Some Siege Tanks and Bunkers provided defense until they Battlecruisers could properly defend the town.

The Terran Battlecruiser Armada engages the evil Protoss fleet of Carriers. Unfortunately the Yamato Cannon upgrade was still researching. A Science Vessel moves in and EMPs the Carriers. The Carrier's commander, realizing his Carriers have no shields, retreats. The Battlecruisers pursue the Carrier fleet and destroy it with only one Battlecruiser lost.

It's all about Repairing
Power Battlecruiser commanding must include a careful watch of the Battlecruisers hit points. When a Battlecruiser starts to become seriously damaged, send it home to be repaired. Usually you want to do that around 200-300 or less (although any number is fine as long as the Battlecruiser is able to make it away safely). Remember Battlecruisers are very slow. Keep this in mind when planning for repairing. Retreat early giving yourself time to get away from the battle in time to repair. Group select your Battlecruisers, when you see one getting severely damaged, click on the box of that unit in the group select window and order it to retreat. This must be done as quickly as possible. Sometimes the enemy will continue to target that damaged Battlecruiser, but if you are lucky, the enemy will pick a new target (with more hit points)

Put as many SCVs on repairing each Battlecruiser as possible. Their high hit points make the Battlecruisers take quite a long time to repair. The more SCVs repairing the Battlecruisers, the faster they will be repaired of course. The time and expense of building Battlecruisers should instill in you a desire to keep them alive. With most other Terran units, it doesn't matter so much when they are destroyed, but when you expend that time and resources in one unit, you must keep it alive.

Repair over Minerals
It is probably best to move the Battlecruisers directly over the SCVs mining Minerals to be repaired. You may find this easier than to pull SCVs off of mining and moving them to the Battlecruisers. You can quickly grab all the SCVs and instruct them using Queues to repair the Battlecruisers. Then you can instruct them to return to mining without having to move them back to the Minerals as you would have to if you moved the SCVs out to meet the Battlecruisers (But both methods work). The Minerals is usually the safest location to repair also, because you should have multiple Bunkers and maybe Siege Tanks protecting the resources. You try moving the SCVs out to another location to repair then move them back to mining but it seems as though it is just easier to repair them over the resources.

Sorting
When repairing a group of Battlecruisers, they are often stacked on top of each other. This can make it difficult to see which Battlecruisers need to be repaired. Consider sorting the Battlecruisers into two groups. Group select the Battlecruisers, and move full health Battlecruisers to a point near the Minerals considered your fixed pile. Keep group selecting the Battlecruisers while they are being repaired. When one is fully repaired move it to the sorted group location. Then as more and more are repaired, your damaged group of Battlecruiser gets smaller allowing you to command the SCVs to repair them more easily. This can be done very quickly with hot keys and some practice.

Formations
You may want to try to compact your Battlecruisers formations as much as possible. If you keep them very tightly packed, they will be harder to individually select to attack by the enemy. But be warned, having them in close proximity also makes them more vulnerable to group attack abilities such as Psionic Storm, EMP, Ensnare, and Plague.

Rotate!
Make sure to rotate your Battlecruisers. The enemy usually fires on whatever ship is at the front of your fleet. You want to keep the units with full health at the front of your formations. Remember at Battlecruiser with only 1 hit point is still as effective and damaging as one with full health if it is in the back firing on the enemy without being hit. Of course, you would want to send this one back to be repaired.

Use the Terrain
Take advantage of high ground. When possible, put your Battlecruisers on high ground firing down on ground targets on low ground where they will have difficulty reaching you. This will allow your Battlecruisers to retreat when damaged to be repaired.

Cloak Detection
Use Science Vessels with your Battlecruisers to spot for Wraiths, Observers and other cloaked units. Use Defensive Matrix on your Battlecruisers to protect them. With 3-4 Science Vessels you can Defensive Matrix 6-8 Battlecruisers allowing them to take on huge armies.

Terran Counters
A small group of Wraiths can easily overcome 3-4 Battlecruisers. To fight Wraiths alone you must have a large group of Battlecruisers or use a mix of both anti-air ground forces (Marines, Goliaths, Ghosts /w Lockdown) along with your Battlecruisers. Be particularly careful to have the ability to quickly counter the Wraiths cloaking through use of Scanner Sweep via multiple Comsat Stations or send a Science Vessel along with your Battlecruisers. You may find Scanner Sweep is much easier to use quickly during a battle, than directing your Science Vessel toward the Cloaked Wraiths. Another worry is Terrans using Lockdown. Use Science Vessels with your Battlecruisers to spot the Ghosts. If your Battlecruisers are locked down, (which is one of the best defenses against Battlecruisers), send in SCVs to repair the Battlecruiser until the Lockdown has worn off. Use the Yamato cannon to destroy Goliaths in one shot. If you plan on beating the enemy with large amounts of Battlecruisers, you will need to be severely out mining the enemy in order to keep up on ground defense and still have enough to produce Battlecruisers.

Protoss Counters
Scouts and Carriers are pretty effective against Battlecruisers. Use large numbers and Yamato cannons to give you the edge. Use Ghosts to lockdown the enemy flyers in combination with your Battlecruisers. Templar's Psionic Storm is something to watch out for. The slow speed of Battlecruisers makes them easy prey to this ability if you are not careful. Use Science Vessels to EMP Protoss Fleets before engaging them. If they retreat, Yamato them.

Zerg Counters
To use Battlecruisers against the Zerg you must have a large number of Battlecruisers. By the time you get your Battlecruisers started, the enemy usually has built up quite a large force of Hydralisks. Unless your Battlecruisers are used in large numbers, Hydralisks make short work of the Battlecruisers. If possible, defend yourself with Siege Tanks and Bunkers until you can build up a sizable force of Battlecruisers. Once you have built up your force, you will work wonders against the Zerg. Large groups of Battlecruisers will cut through large groups of Hydralisks as well as Mutalisks. Battlecruisers do full damage against the Mutalisk. Your main concern will be with scourges. With a small number of Battlecruisers, they easily fall prey to scourges. The enemy may try to divert the attention of your Battlecruisers on other targets, then while they are in firing modes, sneak scourges up to destroy your Battlecruisers. If you do not have a lot of Battlecruisers, use Wraiths and/or Marine support to take extra hits on any Scourges that might attack your Battlecruisers. Also watch out for the Queen's Ensnare ability as well as the Defiler's Plague. Both worth very well against your Battlecruisers. The most damaging defense from the Zerg is Dark Swarm with Hydralisks under it. Run from that attack. Use Irradiate on units under the Cloud. Remember to repair your Battlecruisers.