All this data is potentially out of date, and should be taken with a truckload of salt
A spider tank, or remote repair (RR) battleship gang, is a fleet stratagem where instead of each individual fleet pilot having his own on-board tank, every member of the fleet helps each other with tanking, thus massively increasing the survivability of each member and the fleet's chance of success. A fleet of this type should include at least 20 spider tanking battleships as well as a few tacklers since battleships are slow and should not stray far from each other.
A spider tanked battleship will be fitted as a regular short range buffer tanked pvp battleship but with a few tweaks. Since most of the battleships can have lots of Armor hitpoints while only few can fit respectable shield buffer, Spider tanks are usually based on Armor hitpoints and remote armor repairers.
In its highslots the ship will be fitted with close range turrets or missile launchers such as Autocannons, Pulse Lasers, Blasters or Torpedoes. One or more of the high slots are fitted with Remote Armor Repair Systems (or in a very rare case, Shield Transfer Arrays). The midslots will usually be fitted exactly as a short range pvp battleship with a Microwarp Drive, a Warp Jammer, a Capacitor Booster and, if there are slots left, either a Sensor Booster, an ECCM or a Stasis Webifier according to player preference.
The low slots will, again like the short range buffer pvp fit, have Armor Hardeners, an Energized Platings, Armor plates and a Damage Control. One or two damage modules like Gyrostabilizers or Ballistic Control Units is usually added for more damage. Guideline is to extend the armor as much as possible in order to give his friends time to lock him and apply remote rep while doing reasonable damage. For the same reason, all 3 rigslots usually have a Trimark Armor Pump fitted. Combined, the rigs, plates and Armored Warfare Gang skills can push the ship's armor beyond 35,000 HP.
The strategy of the spider tank fleet is simple in theory but hard to execute in practice. Lag, unconventional enemy tactics and fleet member mistakes are the most significant obstacles to successful implementation. The theory is that rather then repairing their ship or trying to run away, any fleet member that takes damage uses the fleet broadcast window to broadcast "need armor", at which point every member of the fleet uses their own broadcast window to lock their fleet mate and activate their remote repairs on them. This way, a single battleship can potentially be repaired by dozens of armor reps rather then the two he would have in a "normal" set-up and in this way tank a stupendous amount of damage. The set-up has many drawbacks too. The most troublesome one is that fleet members have to stay within 6-8km from each other due to the limited range of remote repair modules. Therefore, while able to tank (for example) a Sniper fleet, the spider tank fleet cannot reach the snipers to hurt them in turn. In actual pvp, individual members can easily drift away from each other due to lag, bumping or warping into Bubbles. Spider tank fleets are most often used against slightly more static targets such as POS and POS modules, Outpost or hostile Capital Fleets.
While not in strict meaning a spider tank fleet, most Capital Fleets consist of many Carriers in support of Dreadnoughts. Carriers, among other things, have bonuses to remote repair modules and any Carrier or Dreadnought under heavy fire can call upon the aid of the rest of the fleet in the manner of a spider tank. A Dreadnought, however, has to complete the cycle of its Siege Modules first, and may be long dead by then.
Small fleets of Battleships with around five pilots can also take part in spider tanking, although the fittings of these ships requires some additional modifications to be effective. At least three 1600mm armor plates are required with smaller numbers to provide a buffer tank while the other members of the fleet are able to lock and set the remote repairs into action. Due to the lower amount of armor repairs being active upon the damaged ship, the greater amount of armor is needed to provide a stronger tank.
There are several problems that can arise when spider tanking. ECM is the most severe threat to fleets of Spider tanking ship, a ship that has been Jammed (Can no longer target) is not capable of providing remote assistance to other ships, lowering the tanking potential of the fleet.
Capacitor or Cap is also a problem with Spider tanking fleets, as pilots with often struggle to maintain a high amount of cap while running two remote repairs as wells as guns. This can be offset by the use of a Cap booster to provide an extra injection of cap when needed.
Communication can also be a problem, as in the heat of a battle it is not always easy to see who is in need of repair and who is not, In smaller gangs a watch list is used to show who is taking the most damage, however in larger gangs the broadcast 'Need Armor' is used. A confident Fleet commander can coordinate repairs but also has other duties to attend to in a Fleet.
The pilots themselves are also a danger to a spider tank. If pilots begin to panic about being shot or jammed, they will lose their ability to concentrate and begin to make mistakes - such as repairing an enemy or shooting a friendly.
Spider tanks were made popular by the Alliance Tournament when some members found it was a very effective way of keeping one ship alive against the onslaught of many. The practice spread through the EVEtv and is now a common sight in 0.0 warfare.