Iron Marines+ Mission 4 Guide: How to Beat Hold the Line

To beat Mission 4 ("Hold the Line" / Infiltration Defense) on Sagan-1 in Iron Marines+, secure the outer choke corridors immediately, hold the front line with Hero Commander Taggins and Marine Troopers, and invest your Ether into turret upgrades rather than unit replacement.

Early Chokepoint Setup and Base Layout

The map centers on a primary command base fed by narrow entry lanes where enemy paths converge. If Fell swarms push past these corridors, they will encircle your central base and split your squad's firing angles.

1. Claim the forward sockets: In the opening minute, construct standard Gatling Turrets on both flanking lanes nearest the entry corridors. Pushing defenses outward ensures alien ranged attackers are intercepted before reaching the central structure.
2. Block the bottlenecks: Station your infantry directly in the narrow corridors. Confining enemy waves inside tight bottlenecks prevents melee swarms from surrounding your troops.
3. Preserve tether distance: Keep your units within retreating distance of base support shields, but do not let enemies fight inside the inner courtyard.

Unit Composition: Marine Troopers and Snipers

Pairing durable frontline infantry with high-damage ranged fire provides the crowd control and armor penetration needed to survive each wave.

• Marine Troopers: Keep at least one full squad deployed at the bottleneck. Their primary job is absorbing melee claw attacks and throwing combat grenades into packed enemy clusters.
• Snipers: Position Snipers behind your Troopers on rear or elevated terrain covering both approach corridors. Direct their fire toward ranged spitters and heavily armored beasts to protect your frontline from sustained corrosive damage.
• Role Swapping: When a wave consists entirely of light melee swarms, temporarily switch a Sniper squad into an extra Trooper squad or Flamethrower team to clear the cluster, then switch back before armored targets appear. Avoid running purely ranged squads, as fast Fell runners will close the gap and overwhelm unshielded Snipers.

Hero Control: Commander Taggins

Commander Taggins serves as your frontline defensive anchor. His high health pool, armor, and steady firepower allow him to hold the corridor facing the heaviest pressure.

• Invulnerability Shield: Trigger Taggins' shield when elite beasts arrive or when concentrated ranged spitters target him. Save the ability for these burst-damage spikes rather than using it on lone minor enemies.
• Offensive Area-of-Effect Ability: Fire his combat drone or missile strike directly into the center of the choke corridor right as incoming swarms compress into the bottleneck.
• Lane Rotation: Move Taggins between the northern and southern lanes as threat levels shift. If his health drops into critical range, pull him behind your Troopers for a few seconds so his shields can regenerate.

Ether Economy and Turret Priority

Spending Ether on permanent defensive upgrades yields better returns than frequently replacing lost units. Pull injured squads back to heal within shield fields to avoid draining your Ether reserves on attrition.

Managing Multi-Lane Attacks and Burrowing Enemies

Later in the mission, the Fell forces launch coordinated assaults from multiple directions and send burrowing units behind your perimeter.

• Split defensive assignments: Hold the secondary approach with an upgraded turret and your Sniper squad to whittle down enemies from range. Place Taggins, your Troopers, and heavy turret fire on the primary approach. Once the main group is defeated, rotate mobile units to clear the secondary lane.
• Counter burrowers without breaking formation: When dirt indicators show enemies surfacing inside your perimeter, leave your Troopers in place at the outer choke points to keep the main wave locked outside. Redirect Taggins or command your Snipers to pick off the internal infiltrators before they damage base structures.