StarCraft: Brood War/Terran Mission 1: First Strike

Meeting Duran
You start with a well-established base with plenty of minerals, but not a whiff of Vespene. You need to find a geyser, so just build a couple Marines, then send your Marines and starting Siege Tanks east. There's an enemy Barracks and some ground troops here. Take it out if you want, but the enemy will keep delivering units via dropship, so don't stick around. Head north to Duran's base.

Destroy the Command Center
Duran's base has a Geyser, which you'll need, and he also informs you about a "back door" to the Dominion base. Set up a few siege tanks and bunkers for defense, but you won't need much else. Crank out siege tanks and marines for support. When you have one group of each, march up the north passage. Just siege your tanks whenever danger threatens, and you'll clear out most of the opposition. The only tricky bit is the buildings on the ridge to the north. You can't target them without a ComSat sweep or by sending units up the ramp to spot them. Still, it's only a few infantry on the ridge. Once you reach the command center, siege your tanks and pound it until it's destroyed.

Destroying the Dominion Base
If you are looking for extra difficulty in this level, you may reach the enemy's Command Center by razing through his base instead of the route that Duran shows you. If you plan on doing this, you need 12 Siege Tanks and 6-8 Goliaths, a ComSat Station and optionally 2 SCVs. You can start by placing Duran in a bunker, and destroy the enemy bunker closest to Duran's base with your Siege Tanks. The next two bunkers in the map have Spider Mines near them, so you need to use your scanner sweep to destroy the mines. Keep your tanks sieged until everything in the way is clear, as you will encounter continuous resistance from Marines, Firebats, Vultures and Goliaths and maybe a couple Wraiths. If you clear out the first few bunkers on your way, you will find that you are now standing on dirt rather than snow. The bunkers there will also have spider mines around them. You are getting close. Try not to receive fire from enemy Siege Tanks in siege mode; you can do this by simply getting them to respond with their own siege tanks. Once the enemy tanks go into tank mode, they will not go back into siege mode. Have your Goliaths protect your siege tanks along the way, especially from Wraiths. Goliaths are very useful against Wraiths since they are larger than marines yet longer ranged. (They can also be repaired!) If you managed to clean up all the infantry in the area, you are well on your way to taking down the Command Center.

Keep in mind, the enemy will deliver units to respond to your attacks via Dropships, so you need your Goliaths close to your tanks at all times. Although the enemy uses a Starport, all air units have been disabled for you.