Hammerhead Gunship
The Hammerhead Gunship is the Tau's analogue to a Tank. Has a distinctly piscine name and can mount railguns.
It can be considered the Tau's "main battle tank", being a general purpose combat vehicle, though its mounted railgun means that it really shines against enemy armor. It has one point less armor in the front than a Leman Russ Battle Tank, but is otherwise similarly fortified. Fluff says that it and the Leman Russ tank are equal. Given the numbers of Leman Russes compared to the number of Hammerheads... probably sucks to be a Hammerhead in the fluff. Unlike the Leman Russ, the Hammerhead is not intended to smash its way into enemy lines, instead hanging back and exploiting the 72" range of its primary weapon to put holes in the Tau's enemies while taunting them to try and rush it. It can be equipped with a disruption pod that gives it a 6+ cover save in the open and 3+ in ruins/fortifications that can help it remain much more survivable than its armor would suggest.
It can take an ion cannon in place of its railgun for the same points value, but without the +5 for the submunition, which will do some hefty damage to heavy infantry and monstrous creatures. Forge World makes some additional primary weapon options, which are all pretty good good, with one major exception *cough*missilepod*unconvincingcough*. Secondarily it is equipped with either a pair of independently targeting gun drones, or a single smart missile system. The gun drones have a shorter range and pinning, but the smart missile system can hit from a slightly greater distance and ignores cover and line of sigh. Most of the time though this is moot unless in an emergency, since the Hammerhead will usually try to stay outside the range of these weapons anyway.
In 4th and 5th Editions, the Hammerhead competed with Broadside Battlesuits for heavy-support slots. For roughly the same cost, a trio of Broadsides could put three twin-linked railgun shots on target compared to the single-shot Hammerhead. However, the Hammerhead could move further before shooting, and could fire an S6 AP4 Large Blast template to vaporize light infantry, while Broadsides could only, at best, bump off three soldiers with a lucky round of shooting. For the 6th Edition Codex, Games Workshop decided to "resolve" the conflict (read: give people a reason to buy both Broadsides and Hammerheads) by changing the Broadside's main weapon to the "heavy rail rifle" -- nerfed to S8, but with the option of getting Skyfire, making them a threat to flyers in a way that a lone Hammerhead never could be.