Sentence:  It's painfully slow and complex work which has never been attempted before in these conditions: the small box-shaped <WSD>robots</WSD>, equipped with two claws, are operating in almost freezing water 5,000ft below the surface, in pitch black and strong currents. 
Meaning of the word marked with <WSD> tags:  A machine built to carry out some complex task or group of tasks by physically moving, especially one which can be programmed.