Anyone who grew up with these books is familiar with this story:
Five teenagers discover that parasitic aliens, Yeerks, are secretly infiltrating Earth by taking over people's minds and bodies. They encounter a good alien, an Andalite named Elfangor, who gives them the power to morph into any animal they have touched. Joined by Elfangor's younger brother and unable to trust almost anyone else, they begin a violent and secretive guerrilla war against the alien invaders.
Along the way, they find allies that they never expected, enemies that prove more dangerous (and bizarre) than the Yeerks themselves could ever be, travel to alien worlds, and confront their own inner conflicts.
This series did aliens right. While so much of scifi plays with humanoid extraterrestrials, the creatures in Animorphs are like nothing on Earth.
KNOW YOUR ALIENS;
Space, the Final Frontier:
It's hard to say what the ultimate capacity of the Yeerk of Andalite fleets are, because they are generally spread throughout space, exploring and harassing each other while running at least eight major campaigns simultaneously. Earth, with a single Pool Ship, single Blade Ship, and double-digit Bug Fighters is considered a sideshow, and when unaware of the presence of the Blade Ship, the Andalites believed a single Dome Ship could easily clear out the Yeerks. Leera, on the other hand, was considered a significant campaign, the Yeerks committed 2 Blade Ships, 4 Pool Ships, and 'several hundred' Bug Fighters. The Andalites had 2 Dome Ships, a couple of assault ships and a third the fighters.
When the Andalites became serious about ending the war in later books, they assembled a fleet of 30 Dome Ships. The Yeerks believed this fleet could curb stomp them anywhere but in their most fortified systems, it was a serious strategic threat, but not treated as an immediate threat to the Yeerk leadership.
When Ax first sees the Blade Ship, he calls it a Visser's ship. If every Visser gets one (not guaranteed) and there aren't any being used except as command ships for Vissers (also no guarantees) that would imply there are 42 Blade Ships in the Yeerk fleet.
Fortunately, some time ago Applegate supported some schematics of Yeerk and Andalite ships online, these were on the series official website back when everybody used dial-up.
For scaling purposes, the Galaxy Tree's Dome was estimated to be half a mile (0.8 km) in diameter. Crew of a thousand warriors, complement of at least 16 fighters. 2 Main Shredders, stated at various points to be capable of "blasting large chunks off a planet" "blasting a hole through a moon" and "incinerating a planetary atmosphere" with a single shot. The first two could be hyperbole, but the last is deadly serious. Shields capable of taking at least a few hits from their own main weapons, armored hull more than 10 feet thick, the least part of which can easily survive reentry.
Powerplant unknown. At one point in the Andalite Chronicles Elfangor claims it takes the power of a medium-sized star to move a ship through Z-Space. Andalites have expressed familiarity with the concepts of fusion and antimatter throughout the series, but never commented whether they use either one. Alternatively, the morphing process somehow draws energy from Z-Space to work, perhaps other Andalite technology utilizes this. Ax claims that nuclear fission is only used in toys, "make little dolls talk and so on."
The Dome Ship is the major, really the only capital ship we see the Andalites use. As per the usual sci-fi idiom, it acts as both a battleship and a carrier for fighters. Aside from the practicalities of Andalites being a race of claustrophobics (all Andalite ships have high ceilings, wide halls, and holograms of the sky) the Dome serves a symbolic purpose. The ship carries a chunk of the Andalite homeworld to remind every warrior what they fight for, and place it beneath an endless view of the stars to remind them how vast the universe is. Most of the time, the dome is not a huge liability, but when the ship needs to fight it separates the dome so it can be faster, more maneuverable, and have wider firing arcs.
The Yeerk answer to the Dome Ship, mostly seen in the series as the command ship of Visser Three. The Blade Ship is a Dome Ship's match in shields and firepower, and is significantly more maneuverable, at least while the Dome Ship still has a dome on. The Blade Ship carries at least 6 Bug fighters, and has a cloaking device that hides it from view and radar, though not from the advanced sensors of an Andalite ship. And yes, it can fire while cloaked.
The Yeerk Mothership. Shaped vaguely like a very rounded beetle, with a flat 'belly' and a tall sloping 'back' plus 3 large legs that go up and back down like a spiders, and dozens of writhing translucent tentacles dangling beneath it. Like the name implies, the Pool Ship mostly contains a very large Yeerk pool and kandrona, carrying enough Yeerks to get a planetary invasion well underway, at least 17,000 Yeerks are in such a ship at one point, and I doubt that was anywhere near its full capacity. In battle, the Pool Ship has a single forward mounted dracon beam powerful enough to threaten a Dome Ship or a Blade Ship, but compared to either of those, it's a tub. It also serves as a carrier for a large (sadly unspecified) number of Bug Fighters, at least a dozen.
Both parties employ a number of freighters, transports, even assault ships. Plus a few generic general purpose spacecraft. The Andalites apparently have a sizeable number of scientific and exploration ships they have mothballed as the war has come to dominate their lives. Most of these have at least a single energy weapon, and even a freighter can score a fighter-kill if the gunner is good or lucky. Yeerks have the trucking ship, which collects air and water under cloak, and is shaped like a manta ray.
Fighters are a touch unusual in this universe. First off, unlike X-wings or Vipers, which are more-or-less like jet fighters that fly in space, Animorphs fighters are about 9 meters long, and as roomy inside as the shuttles in Star Trek. This is both because they are spacecraft, and because both fighter types are FTL capable and are equipped to spend weeks without seeing their mothership. This is frustrating because we can only hazard a guess whether the swarms of fighters at Leera came in the bellies of the capital ships or flew beside them the whole way. It also adds to their flexibility, since fighters can be used to shuttle people to and from orbit. You can also fit a dozen Hork-Bajir in the back of a Bug Fighter and airlift them anywhere you need to. The standard crew is one pilot, one gunner. Both Yeerk and Andalite use this arrangement.
In the 40 year Yeerk-Andalite War, the Andalites come up with at least 8 models of fighter, all using the same basic design, but with small upgrades here and there. We also see the Yeerks a few times experimenting and improving upon Bug Fighters, but the designs remain broadly competitive with each other. Andalite fighters have a single weapon over the main fuselage, like their own tail blades, Bug Fighters have 2 dracon beams, the long spear-like projections. Andalite fighters also have secondary shredders and bombs for attacking ground targets. Both ships can kill each other with a single hit.
There seems to be no limit on sublight speeds, besides how concerned the pilot is over relativistic effects. At Max Burn an Andalite fighter can accelerate from near-rest to 0.1 c (~67 million mph) in 3 seconds. In atmosphere, we see Bug Fighters burn and fly apart when pushing 3500 mph (5600 kph, or just about halfway between Mach 4 and 5) a few hundred feet above the ground. Then again, they aren't really designed for atmosphere.
They also don't really go for tactical FTL jumps. Apparently there's a margin of error of about a million miles regarding where you come out when using Z-Space, enough to not be able to guarantee surprising the enemy before he surprises you.
Thoughts and coments welcome :D
(I could probably drive some poor shmuck insane by rambling on for a couple hours about a sci-fi series almost no one remembers.)