Terran Bio Fundamentals

Overview

Terran is StarCraft II's mechanical, reactive race. This module focuses on timing attacks — pushes designed to hit the opponent at a specific moment before they can field a superior army. Terran timing attacks revolve around the bio composition: Marines, Marauders, and Medivacs, backed by the Stimpack and Combat Shield upgrades.

Core Bio Units

Marine

• Cost: 50 minerals — Supply: 1 — Requires: Barracks
• Role: The backbone of Terran bio. Exceptional damage-per-cost, but low HP. Marines are most effective in large numbers and with Stimpack active.
• Key upgrades:
  • Stimpack: Increases attack speed and movement speed for 10 HP per use. Researched at a Barracks Tech Lab.
  • Combat Shield: Adds 10 HP to every Marine permanently. Drastically improves survivability against splash damage.

Marauder

• Cost: 100 minerals, 25 gas — Supply: 2 — Requires: Barracks + Tech Lab
• Role: Durable frontline unit. Slows armoured targets with Concussive Shells. Acts as a shield for Marines in bio pushes. Stimpack also benefits Marauders.
• Key upgrade: Concussive Shells — slows armoured units, preventing kiting and enabling easier kills.

Medivac

• Cost: 100 minerals, 100 gas — Supply: 2 — Requires: Starport
• Role: Heals bio units in combat (27 HP/sec), dramatically extending their survivability. Also used as a transport for drops into the enemy base.
• Ability: Ignite Afterburners — a speed burst used to escape danger or close distance quickly.

Barracks Add-ons

A Barracks can attach one of two add-ons:

A standard bio setup is one Barracks with a Tech Lab (for Stimpack) and additional Barracks with Reactors (for high Marine output).

The Orbital Command

The Orbital Command is upgraded from the Command Center and is Terran's most important economic tool.

• Call Down: MULE (50 energy): Drops a mining robot that harvests minerals at roughly 4× the rate of an SCV for 64 seconds. Always spend your energy on MULEs — never let energy sit at 200.
• Scanner Sweep (50 energy): Reveals a chosen map area, including cloaked and burrowed units. Use sparingly, as MULE income almost always takes priority.

Supply Depot

Supply Depots provide 8 supply each. Critically, they can be lowered underground, allowing friendly units to walk over them. This is used to wall off your ramp — a wall of Depots and a Barracks blocks all ground units, and lowering one Depot creates a gap you can control. Terran players also use raised Depots to block enemy units from entering the base during an attack.

Builds, Timings, and Execution

What is a Timing Attack?

A timing attack is a push designed to hit the opponent before they can respond with a stronger army, better tech, or more units. Every game has windows — moments where one player is temporarily more powerful than the other. Terran timing attacks exploit those windows precisely.

The timing attack does not have to kill the opponent. Forcing them to pull workers, cancel expansions, or divert units away from the front is often enough to create a decisive advantage.

The Reaper

• Cost: 50 minerals, 50 gas — Supply: 1 — Requires: Barracks + Tech Lab
• Role: The best early harassment and scouting unit in the game. The Reaper can jump up and down cliffs using its jet pack, reaching locations other units cannot.
• Reaper HP regenerates passively over time — it is difficult to kill unless the opponent commits hard to chasing it.
• The Reaper is never the kill shot. Its job is to damage workers, force defensive spending, and gather information about the opponent's build.

The Reaper Expand Build

The Reaper Expand is one of Terran's most common and versatile openings. It combines early harassment and scouting with safe economic development.

Build order:

1. Build Supply Depot (at 14 supply)
2. Build Barracks (at 15 supply)
3. Build Refinery
4. Build Tech Lab on Barracks → Produce Reaper
5. Float Reaper to opponent's base — harass workers, identify opening build
6. Build Command Center (float it to natural when ready)
7. Build Orbital Command on main, lower the natural Command Center
8. Build Reactor on Barracks → start Marine production
9. Continue SCV and unit production

The Reaper gives information that shapes your next decision: if the opponent is going for an early rush, you adjust; if they are playing greedy, you apply more pressure.

The 2-1-1 Build

The 2-1-1 describes the production buildings: 2 Barracks, 1 Factory, 1 Starport.

This is the backbone of most Terran bio timings. The goal is to produce Marines rapidly from two Barracks while the Factory and Starport provide the Medivac for a drop or timing push.

Approximate production structure:

• Barracks 1 + Tech Lab (Stimpack and Combat Shield research)
• Barracks 2 + Reactor (double Marine production)
• Factory (used primarily as a gateway to unlock the Starport — produces 1 Hellion or Reaper, then lifts off)
• Starport → produces Medivac

The first timing attack typically arrives at 6:00–7:00, timed around when Stimpack finishes.

Stimpack Timing Push (~7:00)

This is Terran's most iconic early-game timing. When Stimpack research completes, your bio army's combat effectiveness roughly doubles. Hitting the opponent in this window — before they have enough units or tech to respond — is the goal.

What you bring: 8–12 Marines, 2–4 Marauders, 1–2 Medivacs Target: Natural expansion or main ramp Goal: Force significant economic damage, kill the natural expansion, or close out the game

Use Stimpack proactively in the fight, not reactively. Medivac healing offsets the health cost. Spread Marines slightly to reduce splash damage.

Marine-Medivac Drop (~5:30–6:30)

Before or alongside the ground push, a Medivac loaded with Marines dropped into the opponent's mineral line creates chaos and forces a response. Workers are fragile — even 4 Marines in a worker line can kill many workers before the opponent can react.

The drop is a distraction and an economy hit. It forces the opponent to choose between defending the drop and holding the main push.

Execution tips:

• Load 4–8 Marines into the Medivac
• Drop into the mineral line (not the middle of the base)
• If uncontested, attack workers — do not attack buildings
• Boost (Ignite Afterburners) away when anti-air arrives

Build Order Summary

Standard 2-1-1 into Stimpack timing:

1. Build Supply Depot (14)
2. Build Barracks (15)
3. Build Refinery (16)
4. Build Orbital Command when Barracks finishes
5. Build Tech Lab on Barracks → start Stimpack research
6. Build second Barracks with Reactor
7. Build Factory → build Starport → build Medivac
8. Attack when Stimpack finishes (~7:00) with Marines, Marauders, and Medivac support

Keep producing Marines throughout. Never let your Barracks sit idle. Call down a MULE every time your Orbital has 50 energy.