Underground Cave

Underground Cave is the sixth mission in Earth Defense Force 2025 and Earth Defense Force 4.1: The Shadow of New Despair. It introduces Spiders, is the first time the Tactics Officer speaks, and is the first tunnel mission.

Objective
2025: A giant bug nest has spread out under the city. We cannot allow it to remain intact! We will now start to infiltrate their burrows. Move out immediately and report to the local Ranger team for further instructions.

4.1: A giant insect nest has spread out under the city. We cannot allow it to remain intact! We must begin infiltrating their burrows. Move out immediately and report to the local Ranger team for further instructions.

Storyline
Storm Team and a squad of Rangers are sent to investigate the nest with the goal of destroying it, to prevent the insects from continuing to evolve. The entrance to it turns out to be accessible through a freshly-dug tunnel in the back of a shopping mall. This leads into an underground train station immediately below, the train tunnel quickly leading into the massive chambers of a nest it is astonishing nobody noticed any earlier.

HQ, who is back from his unexplained break for most of the last level, is apparently still buying into Ohara's idea that these giant insects are survivors of the 2017 war even though it has been established they are doing something that requires they reproduce, and can't believe there are so many. EDF soldiers are already wary of the sheer scale of the nest, with one working out that they are increasing in number, while another declares that if they are not dealt with soon, mankind will be destroyed.

Meanwhile, some offscreen EDF soldiers are astonished that some mysterious creature "survived...after all that?!" and soon are reporting doing battle with "giant spiderlike bugs", and that they are being attacked with thread. "It's no use, they got stronger!" they say, of enemies with less health than the ones they have been fighting prior to this. At the very least, two entire Ranger teams, 21 and 12, are soon wiped out, and the EDF forces request permission to retreat as Storm Team comes face to face with a large group of the "giant spiderlike" Spiders.

Ohara is horrified as reports of casualties pour in, seemingly having forgotten about Spiders being part of the Ravagers' giant insect forces in the 2017 war as well. He becomes despondent, whimpering "what is this, what is this?" and wondering if all of his preparations were in vain.

HQ, as ever bold as brass and about as intelligent, snaps him out of it, declaring there is "no room for defeat!" He has already requested backup from the Air Force in the form of the heavy support aircraft Whale. This does little to help ease the fears of Storm Team, who are in fact still underground. The Tactics Officer, one of the few EDF officers who are professional and sensible, speaks for the first time as she confirms the Artillery Team's self-propelled howitzers and rocket launchers are also on the way. HQ finishes with a defiant "The fight starts now!"

4.1 Changes
As with all underground levels, this level is now dark, making it harder to spot approaching enemies, and the Air Raider can now call for the Depth Crawler or SDL1 rather than having no support available. Neither vehicle is incredibly useful since the Depth Crawler is fragile and jittery to control, though some models have reasonably good weapons, while the SDL1 is the SDL1.

HQ has an extra call to "turn on your helmet lights" at the start of the mission and near the end of the train station notes that Depth Crawlers can light up dark areas, ordering Air Raiders to call for Depth Crawlers. Some jocular NPC dialog is added immediately before the third wave of Ants to acknowledge that the level is now dark, with one EDF soldier trying to creep out another (and succeeding), while a third cheerily declares it the "best haunted house ever."

Enemies
Both versions:

3 waves of black Ants, 10, 27, 31

1 wave of Spiders from two locations, 48 in two groups of 24.

Both Versions
The first underground level is a taste of what is to come in such missions. Since these mission include a lot of close-range combat, it is wise to leave the sniper rifles and mortars at home and focus on bringing an effective direct-fire splash damage weapon and an effective automatic or spread weapon. Flame weapons are good, the Ranger's napalm guns even better, and his Flame Geyser weapons (which can shut down entire tunnels) best of all. The Wing Diver is at her strongest in tunnel missions where her Idunn and Thunder Bow weapons truly shine, while the Fencer has trouble with them (especially if the player has not figured out that firing two flame revolvers at once is only a good idea if they are highly interested in the ceiling) and the Air Raider in 2025 has even more since he cannot call for vehicles underground. Shield walls and ZE-Gun turrets or one of the Limpet Splendor ricocheting flechette weapons are his best bet. For fairly obvious reasons, he also cannot call for artillery of any kind.

There are actually three tunnel maps, and the color of the walls indicates which one the player is in: this one has muddy walls, the later Cave map grey walls, and the last has swirl-patterned orange-brown walls and only appears twice.These maps are varied by adding stony-looking grey "plugs" or piles of rubble in various locations to seal off portions or create self-contained mini-maps; here, plugs are placed to prevent the player going deeper into the nest than the main room and its side-chambers, and extensions of the subway tunnel that go further under the mall and beyond the area of the main room are blocked with rubble.

Since enemies are funneled by the level layout, it is fairly hard for them to sneak up on Storm Team, though the player should be wary that the subway tunnel continues into the room where the third wave of Ants spawn and is right next to the room where most of the Spiders spawn. While unlikely, it is possible for enemies to sneak up from the side using this, though more normal to just find one or two stragglers lurking uselessly about halfway along the tunnel when the main horde is gone. If a lot of the NPC Rangers develop a deep desire to shoot the left-hand wall of the tunnel into the main room, it means there are bugs in the subway tunnel (and in the Ranger AI). Going this way rather than following the NPC Ranger unit is a bad idea since as noted, the larger part of the wave of spiders spawns in the chamber near the subway tunnel's end.

The NPC Ranger unit cannot be recruited unless the leader dies, and follows a pre-set route leading to the main chamber, with scripted dialog at fixed points along the way.

Ants encountered in tunnels will tend to approach in wide groups on the floor or ceiling; if alone, they will tend to walk in spirals.These broad groups allow many ants to attack at once and deal a lot of damage, though a Fencer can have a ball using his Deflector to kill them with their own acid spray.

The Spiders are a new challenge, unless the player is familiar with previous EDF games, in which case they are not. They are weaker but faster than Ants, move mostly by jumping, and use a thread attack similar to that of the Retiarius already encountered. However, this is launched on a flat trajectory from closer range, and simply does one-off damage. As with the Retiarius, as long as threads are visible they can still deal damage, though Spider threads that have already hit something other than terrain are no longer "live." The Fencer can still reflect this attack, though the timing is tighter as it must be done while the threads are still airborne.

Unlike 2017, normal spiders do not have any intentional ability to fire through walls, regardless of difficulty, though tunnel missions do have some glitchy geometry that allows them to do so in certain places anyway. This is tightened up in 4.1.

The wave of Spiders enters the main chamber of the level from the left and right; it is wise to greet them in the downward-facing tunnel where the third wave of Ants were fought, since among the rocky pillars of the large room it is very easy for the fast-moving Spiders to flank the player or attack them from above.