TOMTIT was an acronym for Transmission Of Matter Through Interstitial Time, and was created at the Newton Institute by Stuart Hyde, Dr. Ruth Ingram and Professor Thascalos (an alias of the Master). TOMTIT could break down solid objects into light waves and transmit them from one place to another, much in the same way as a teleport or transmat.
The Master altered TOMTIT to act as a time travel device (much like a time scoop) and pick up elements of Earth's military history to fight against UNIT when they attempted to remove him from his base of operations. Through repeated use, he summoned the Chronovore known as Kronos and an Atlantean named Krasis. (TV: The Time Monster)