Adam Hart-Davis cycles around the country in search of the unsung heroes of science.
This week he visits London, where he builds his own submarine to illustrate the achievements of Cornelus Drebbel, who rowed underwater from Westminster to Greenwich and back again.
His other subjects include Charles Babbage, whose work with mechanical adding machines heralded the computer age.

Local Heroes Kit: a cheque for £9.95 payable to BBC Education, to [address removed]. Or phone [number removed]. Calls charged at national rate.