The Umigumo or “Kumo” appears to be the Chimeran army’s standard assault vehicle and primary counter to the Grampus. It is armed with torpedoes, needle guns and pressurized cannons mounted on its two claws. Being an amphibious machine, it can engage in combat in both ground and underwater environments.
The performance of this machine against the Grampuses seems rather lacklustre and weak however. The Umigumos appear to be fragile machines; easily outclassed unless in large numbers, and easily torn apart by sub-launched shrapnel torpedoes (see EP1 and EP4), and hand grenades.
Though the character bios noted that Mutios are the Umigumo’s ‘ultimate’ pilots, this is not evidence that the machines are piloted by them exclusively. I personally believe that they are piloted by various Chimera, with the Mutios being the most elite among them. It doesn’t seem to make sense to designate the females and ‘mothers’ of a species into such a dangerous role.