The early game of a TvP match up is dictated mainly by the quality of scouting. Protoss has a wealth of tech paths and build orders they can choose from that can apply pressure or outright kill the terran if there’s insufficient preparation. Therefore, unless you’re willing to risk wasting a scan, a reaper opening is very favourable, since this unit is quick, jumps cliffs and regenerates health rapidly. The reaper’s sole job is to scout, not to kill probes.
The reaper scout requires an early refinery to be taken, so that the terran can afford the 50 mineral, 50 gas expenditure for the reaper. After this, the terran player has a decision; either take workers out of the refinery to mine minerals to afford more barracks or a quick 2nd command centre (or even a greedy 3rd command centre) or keep workers in gas to build a factory.
The standard 3 barracks opening does have some benefits in comparison to a factory opening, the main one being that the terran has more units in the early game to fend off any kind of early attack or to be aggressive with more units once stimpack and medivacs are available. The factory based opening can lead to early game damage (depending on the skill of the protoss opponent), easy defence against oracle openings and could lead to a hyper aggressive drop-based mid-game. Furthermore, should the protoss player have chosen a twilight council tech path, detection will be delayed, allowing widow mines to more potency.
The basic build order is as follows:
|21||04:50||Constant marine production (upon completion of reactor)|
|32||05:55||Supply depot (beyond this point, assume constant depot production)|
|46||06:55||Tech lab (on the factory)|
|50||07:10||Tech lab (on the starport)|
|50||07:10||Carry out a widow mine drop|
|56||07:40||Remove factory and starport from their respective tech labs|
|58||08:00||Move the two newly completed barracks onto the tech labs|
|60||08:20||Research stimpack and combat shields|
|64||08:35||Research +1 infantry weapons|
|66||08:45||Assume constant marauder production|
|70||08:50||Reactor (on the starport)|
|101||10:25||Carry out a double medivac drop|
Upon completion of 3rd and 4th medivac, carry out another drop.
While harassing your opponent via medivac drops, the priority is to not lose the medivacs. Should your opponent select the collossus tech path, vikings must be made from the starport and if medivacs have been lost prior to this, your medivac count will be greatly reduced, impairing your healing potential.
By dropping your opponent, you not only may cause great damage via killing probes or key tech structures, but also hinder them from safely taking a third base.
Upon taking your third base, your minerals will begin to increase rapidly, despite constantly building from your barracks. At this point, three more barracks should be made, increasing the total barracks count to eight.
Your infantry composition should be 50% marines and 50% marauders. Therefore, three of your eight barracks should have reactors and the other five should have tech labs.
If fighting against a templar opening, widow mines and ghosts would be a great addition to the overall army composition to rapidly eradicate all the zealots of the opponent/ deplete the high templar of energy.
If the opponent should be going for an aggressive gateway attack, their detection (observers or oracles) will be greatly delayed. Therefore, you must build several bunkers, repair when necessary and drop harass post-attack.