"Cool! The fun level is rising rapidly!"
For legal rather than narrative reasons, the Fuchikomas of the Ghost in the Shell Manga were replaced by Tachikomas in the Production I.G. Stand Alone Complex series. The Tachikomas appear to be highly experimental devices in use exclusively by section 9 (in one episode, an ordinary police officer fails to recognise them as police/military kit and assumes the 10 ton tank to be a toy belonging to the young girl it is accompanying!).
On the hardware side, they feature 4 legs (with wheels for higher speed movement on roadways; the walking sound implies considerably greater bulk than their appearance would suggest), two manipulating arms (with guns), a main gun (either a cannon or gatling-style depending on the model), 3 spheres that facilitate vision, a passenger section capable of carrying one team member, stealth capability through thermoptic camouflage and the ability to shoot and hang from threads, spider-like.
Of considerable more interest are the software aspects of the Tachikoma. Spoiler Warning from here-on in! As Stand Alone Complex runs in parallel to the Ghost in the Shell movie (also by Production I.G.) rather than as a sequel, we can conclude that self-aware AI such as the puppet master has not yet emerged; more succinctly, there is no ghost in the shell. The Tachikomas represent an experiment in emergent artificial intelligence but make no claims to having a ghost. Designed with a child-like innocence and mannerisms their constant acquisition of information leads to emergence of personality. In the film, Kusanagi's interest in the puppet master arose from her own self-doubt born out of fears that were a program able to generate its own ghostline, then as a cyborg she may have unwittingly lost all humanity long ago. With the primary protagonist in SAC being the Laughing Man (who although mysterious doesn't seem to be intended to be an AI) the opportunity for debating such issues arises instead from the Tachikomas.
Thus, whilst the childish voices of the Tachikomas may grate for some (they have been accused of spoiling the atmosphere of the GitS universe; yet they are in fact in line with the manga), they are there to make a point rather than up the cuteness factor. The bottom-up idea of causing AI to emerge by creating a system able to learn (akin to the development of children), rather than a top down approach of codifying intelligent behaviour and somehow implanting it in a machine, is not a new one. When presented with 'real-world' problems such as the task of crossing a cluttered room, simpler systems that seek to unwittingly imitate the competence of insects can outperform those that are designed to in some sense comprehend the situation and then reason their way through (see Steven Levy's Artificial Life which in part considers these issues with respect to robots from the MIT Mobot group.) In a similar vein, the Tachikomas seem to have been given a lot of tools but little direction in how they should be using them, instead accompanying section 9 and often fending for themselves. They certainly show more versatility than the standard secretarial androids that are used in the section- on one occassion, deliberately crashing one with the epimenides' paradox so that they can steal a computer to play with!
A particularly touching episode which focusses on the Tachikomas is Episode 12 - Tachikoma Runaway: A Movie Director's Dreams. Batou's "All natural oil" seems to enhance their curiosity, so when his favourite Tachikoma gets bored it heads out into the streets in search of entertainment (from where the quote at the top of the node comes from). Once there, it joins up with a young girl, Miki, in her search for 'Locky', her dog. As Tachikoma blunders its way through town (picking up a random dog then throwing it away; advising against fast food, stealing a cyber-brain and impersonating a military hero) it slowly transpires that the dog is dead, and that Miki was aware of this all along but her parents had been trying to shield her from the truth. The Tachikoma can't comprehend death, but does seem to understand sadness at separation. As Miki sleeps in the passenger section during the drive back, the screens inside ponder "To be...not to be".
The learning process is enhanced by the fact that all the Tachikomas are synchronised each evening. The extent of this process is unclear however, and raises the need for some interesting distinctions. Primarily, divisions need to be drawn between experience, knowledge and personality, and it is the acquisition of the latter which causes Kusanagi to consider them unsuitable for their role as combat devices (and their eventual removal from use within section 9).
For instance, Batou has a favourite Tachikoma, but after a daily synchronisation, none of the Tachikomas knows which of them it is! In essence, all the experiences the Tachikomas have over the course of a day add to their individual knowledge, but this knowledge is then shared between them so they have the same associations- each believing that they had the original experience. If it is felt that personality arises purely from this set of knowledge and associations, then it could be argued that they should all act identically. However, they often have arguments amongst themselves (which otherwise would be internal?), and of particular interest is one Tachikoma which spends all its time reading books (such as Flowers of Algernon). Presumably if one enjoys reading then after synchronisation all the others will have favourable associations with that day's book. It's unclear whether the same robot settles down to read each day or if they truly lack individual personality and different ones take this role (they could all have the same set of responses, but weighed by arbitrary factors such as the order in which they get back from training). Much of this theorising is made difficult by the fact that they have identical paint jobs, but ultimately playing with the ideas is more fun that trying to find the 'right' message that SAC is trying to convey.
A major theme for the Tachikomas is the development of their concept of death. They consider that death would be meaningless to a machine without a ghost- but then they realise that being wiped clean would lead them to lose treasured associations, such as fond thoughts of Batou or Miki. This fear of losing attachments leads them into deliberately acting more like the less mentally agile machines used in the section rather than risk being considered intelligent and hence removed. Yet despite those concerns, they are prepared to sacrifice themselves fully for those they display affection towards- at the end of the series, 3 Tachikomas launch a suicide mission (at Kusanagi's direction) to help save Batou. By this point they had ceased to be part of section 9, and thus could not rely on the distributed nature of their memory to preserve unique experiences- yet they are driven by something I would consider akin to emotion to act selflessly.
More comically, most of the episodes feature a short (90 seconds or so) sketch after the credits with the Tachikomas in a matrixesque white construct. Sometimes they refer to events in the episode, in others they have unrelated conversations -e.g. about the nature of human conversation or reading books as methods of communication.) Sometimes they just play frisbee, shoot each other or explode in various ways. Most of these went right over my head, but they're sweet!