Type 40

Type 40 was the class of TARDIS to which the Doctor's TARDIS belonged.

History
The Monk said that while the Doctor had a Mark I, the Monk himself had a Mark IV. We do not know if the Type 40 belongs to a Mark I class of TARDIS or whether Type 40 had more than one Mark. More probably the latter, as the Doctor found the technology of his own TARDIS almost entirely compatible with the Monk's. Also, the central consoles of the two craft looked almost identical, although the Monk's ship had a slightly taller supporting column. (DW: The Time Meddler)


 * The Master also possessed a more advanced TARDIS, though we do not know of what type.

By the time of the Doctor's fourth incarnation the Type 40 was obselete and except for the Doctor's own Type 40, had been decomissioned (DW: The Deadly Assassin). Romana also noted the fact of the Type 40's obsolence (source?)

Properties
Except for its capacity to dematerialize and rematerialize at will into the Vortex the TARDIS' outer plasmic shell had the properties of a solid object. Using its chameleon circuit, it could change shape. The TARDIS seemed to weigh roughly the same as the object it was disguised as, rather than manifesting the immense theoretical weight the interior possessed. On several occasions the Doctor's ship was picked up and moved using only manual labour (for example DW: Full Circle, DW: The King's Demons) while when resting on an uneven surface it could relatively easily be blown over by high winds (DW: The Curse of Peladon).

Possibly due to some property of the chameleon circuit or its nature as an interdimensional construct, the Doctor's ship was almost always depicted as impervious to brute force attacks of all kinds and effectively indestructible. However, the Sensorites were able to cut the lock out of the external shell, effectively sealing the vessel - why the ship was vulnerable to what appears to have been only a simple energy cutter is unknown. The immense gravity field generated by the Tractators on Frontios initially warped the TARDIS interior before actually ripping the vehicle apart. Time Lord technology was also able to force entry relatively easily on a number of occasions. (DW: The Sensorites, DW: Frontios)

The Doctor described his Type 40 on many occasions as sentient. Therefore some empathy must exist between the user and the machine. (PDA: Heart of TARDIS). During one crisis, the Doctor's ship caused its crew to panic and behave irrationally and to manifest clues to as the emergency, such as melting clocks. (DW: The Edge of Destruction)

Travel
The Type 40 had time travel and space travel ability, via the Time Vortex.It could hover in the air (DW: Fury from the Deep, Logopolis) or fly through space like an aircraft or spacecraft. While this mode it often spun, like a top. (DW: The Parting of the Ways, The Christmas Invasion) It could land on water and float. (DW: Fury from the Deep)

Limits
A properly piloted and working Type 40 was capable of transporting its occupants to almost any point in space and time. One account says that a Time Spiral corresponding to the end of the Humanian Era prevented craft from travelling too far into the future (MA: The Well-Mannered War). Another has shown the Doctor's TARDIS travelling to more than five billion years CE without difficulty (DW: The End of the World, New Earth). A Type 40 can go out beyond the edges of the universe. (DW: Logopolis). More recently, in (DW: Utopia, the TARDIS travelled over 100 trillion years into the future, beyond where any Time Lord had been known to venture. However, Captain Jack touched the TARDIS at the point of dematerialisation, so whether this caused the TARDIS to behave abnormally is unknown.

Pressing an emergency switch, the Doctor found himself in the Land of Fiction (DW: The Mind Robber). The Doctor believed that his TARDIS could materialize inside areas of the psyche. (DW: The Chase)

Before the destruction of Gallifrey, the Doctor, using the console of the TARDIS alone, found himself in an alternative timeline (DW: Inferno). Later, he said that the death of the Time Lords made crossing between worlds almost impossible. (DW: Rise of the Cybermen)

Basic defenses and temporal grace
A hostile Zarbi could not enter the Doctor's TARDIS, as if the ship itself would not allow it. (DW: The Web Planet) When the Shadow attempted to do so, the doors of the ship flooded with blinding light and stopping him. (DW: The Armageddon Factor)

The Doctor claimed that the interior of the TARDIS existed in a state of temporal grace where the Doctor's enemies could not hurt him. The exact nature and area of this effect has varied. One account claims that within a TARDIS it is literally impossible to die from unnatural causes, with anyone so killed being instantly resurrected (PDA: The Infinity Doctors). More commonly, energy weapons were simply rendered inoperative (DW: The Hand of Fear, DW: The Invasion of Time) and even then the effect seemed limited only to the console room.

On many other occasions it seems that no such defense existed. Cybermen (DW: Earthshock, Attack of the Cybermen) and a Dalek, for example, have discharged their guns in the TARDIS. (DW: The Parting of the Ways)

Lock
The Doctor initially stated that there were multiple tumblers within the single TARDIS lock presented to the outside world. There were a total of 21 tumblers, and insertion of the key into the wrong ones would cause the entire assembly to melt, barring access to the TARDIS entirely. (DW: The Daleks)

As mentioned previously, the Sensorites were able to cut the lock from the TARDIS' outer shell, sealing the ship until the lock could be reinserted. (DW: The Sensorites)

Sabotage by the Monk later badly damaged the original complex lock system, which the Doctor replaced with a much less sophisticated lock. (DW: The Daleks' Master Plan)

Another account shows the Doctor removing the lock, but having to first disconnect the Time Rotor. With the lock removed almost anyone could walk into the TARDIS. (EDA: War of the Daleks)

There is some evidence to suggest that TARDIS keys are not vessel-specific (the Doctor was able to use his own TARDIS key to enter the Rani's ship). (DW: Mark of the Rani)

Isomorphic controls
The Doctor claimed to Sutekh that the TARDIS has isomorphic controls which would work only for him and no one else. (DW: Pyramids of Mars)


 * The Doctor almost certainly lied to Sutekth, however, as many other people have since used his TARDIS before and since without permission.

Emergency measures
Type 40s had many defensive devices, designed not only to protect the occupants, but also the ship itself. They included the HADS system (Hostile Action Displacement System) (DW: The Krotons).

It was also capable of "anchoring" itself onto another ship to not only stabilise itself, but also to allow the occupants to escape in the event of terminal instability ("break-up") This is invoked by an automatic safety cut out. (DW: Terminus)

Eye of Harmony
The Doctor's TARDIS had a (symbolic) link with the Eye of Harmony and so derived its power from there. (DW: Doctor Who: The TV Movie)

Matter-energy conversion
The ship had, at one time, an ancillary power station, which on the Doctor's TARDIS existed in the form of an art gallery, the exhibited works apparently being converted from matter into raw energy when required. (DW: The Invasion of Time)

The TARDIS's architectural configuration controls could also delete room, apparently converting them and their contents into raw energy which was then dumped into the reactor core. This action could give the TARDIS the added thrust it might need to escape from areas of gravity strong enough to otherwise defeat the TARDIS's helm controls. (DW: Logopolis, Castrovalva)


 * These systems appear to act on a very sophisticated application of the energy-mass equation formulated by Albert Einstein as E=mc2, which among other things, demonstrates that energy and matter are different forms of the same substance, and one can be converted into the other.

Temporal rifts
After the destruction of Gallifrey, the Doctor recharged his ship with the energy from a temporal rift, in this case, the Cardiff rift. (DW: Boom Town)

Other means
Once separated from the main universe on Pete's World the Doctor's Type 40 "died". After finding a glowing green crystal, the Doctor breathed on it, giving it, he said, ten years of his life. Within twenty-four hours, he said the TARDIS had enough energy to return home. (DW: Rise of the Cybermen)


 * We do not know how or why the Doctor's TARDIS lost its power when separated from the main universe.

Required elements
Elements needed for the proper functioning of the Type 40 and requiring occasional replenishment include mercury used in its fluid links (DW: The Daleks, The Wheel in Space) and the rare ore Zeiton 7. (DW: Vengeance on Varos)

When the Doctor's TARDIS accidentally visited a parallel universe, it could not take its crew back immediately because its energy supply stemmed from the universe it was created in, so by removing it from its home universe its "life" energy supply was severed. (DW: Rise of the Cybermen)