The War Machines

The War Machines are fully armed mobile computers, which look like miniature tanks, which were constructed on the instructions of WOTAN. The Doctor reprogrammed one of them to destroy its creator and deactivate the other machines.

WOTAN is The Will-Operating Thought Analogue, and it was the ultimate self-reasoning computer built by Professor Brett and housed in the Post Office Tower. Having brainwashed his creator, the machine gained control of Polly, Dodo and many other humans through the telephone. WOTAN wanted to rule the world by linking programmed computers worldwide. To rule the Earth, it created War Machines. 

The War Machines only appeared in The War Machines.