Iron Marines+: How to Beat Underdark Heist on Veteran

To beat the Underdark Heist challenge on Veteran difficulty in Iron Marines+, advance through the cavern tunnels incrementally, lure subterranean ambushes back to prepared defensive positions, and eliminate ranged acid spitters before engaging melee swarms.

Recommended Squad Composition

Veteran difficulty features high enemy density and surprise spawns that burst directly beneath your units. Bringing a balanced strike team ensures you can absorb rush attacks while quickly melting high-threat targets.

Unit Class	Primary Role	Tactical Advantage
Brawlers / Guardians	Frontline anchor	Absorbs melee rush attacks and keeps burrowers off ranged units
Flamethrowers / Pyros	Swarm suppression	Clears dense alien packs through narrow tunnel corridors
Snipers	High-threat elimination	Picks off ranged acid spitters and armored targets from a safe distance
Combat Engineers / Mechs	Utility and zone control	Provides passive support, repairs, and sustained auxiliary fire

Place heavy frontline units slightly ahead of your ranged damage dealers at all times. Do not scout forward with unprotected ranged squads, as subterranean ambushes will overwhelm them before they can fall back.

How to Handle Tunnel Ambushes

Moving through the cavern triggers predefined script points where alien packs emerge from the front and rear. Never push into unexplored ground while fighting an active wave.

To clear ambush zones safely:

Bait with your hero: Move your hero forward just far enough into the fog of war to trigger enemy burrow animations or draw nearby packs.
Kite back to your fireteam: Immediately retreat to your deployed squad to force the chasing aliens into your defensive firing arc.
Establish intersecting fire: Hold melee rushers at the chokepoint with your frontline while your ranged units focus down backline threats.
Destroy stationary nests: Once the ambush wave is cleared, move up immediately to destroy nearby egg clusters and hives before they spawn additional reinforcements.

Target Priority Order

Failing to prioritize high-damage enemies will quickly deplete your squad's health pools in narrow corridors. Direct your attacks in this order:

Acid Spitters: Target these ranged artillery beasts first using snipers or hero burst abilities. Their lingering acid pools restrict your movement and deal heavy damage across stacked squads.
Armored Bruisers: Use armor-piercing rounds and hero damage skills to burn down these durable targets once artillery threats are eliminated.
Melee Swarmers: Allow passive cleave, flamethrower cones, and standard defensive fire to clear basic swarming fodder while focusing your direct commands on higher-tier threats.

If subterranean burrowers spawn behind your line, redirect your frontline units immediately or deploy an area-of-effect crowd control skill on top of your ranged units to break the attack.

Securing the Final Extraction

The final sector contains the heaviest concentration of elite enemies in the mission. Rushing directly into the objective triggers multiple spawn tunnels at the same time.

Before triggering the final stand, ensure all squads are reinforced and your hero's major cooldowns are ready. Anchor your frontline at the narrowest tunnel mouth to bottleneck incoming melee waves, and save hero stuns or burst abilities for armored elites as they enter the chokepoint. If a squad member dies, fall back slightly to clear the immediate threat before calling in replacements into a secure pocket.