John David Gwynn (13 July 1907 – 21 November 1998) was a civil engineer with a special interest in renewable energy generation.

As the second World War continued he was put in charge of building the Churchill Barriers in Scapa Flow, Orkney, a task which occupied him from 1942 to 1944.

After his retirement from Balfour Beatty David Gwynn turned to the field of renewable energy, where with characteristic vigour and enthusiasm he proceeded to undertake research and develop innovative experimental designs.

With his team he mounted trial schemes for various small scale stream-driven turbines as well as much larger tidal power devices, and he continued this voluntary work right up to the end of his life.

They had two children: Lee Penelope, a teacher and local government politician, and Robin David, an academic historian and philatelist.