In which 1968 serial did the Sonic Screwdriver first appear?

The Sonic Screwdriver first appeared in the 1968 Doctor Who serial Fury from the Deep. It was used by the Second Doctor, played by Patrick Troughton, as a compact tool for opening locks and manipulating machinery.

Written by Victor Pemberton, Fury from the Deep is set aboard gas rigs and a refinery complex threatened by a sentient seaweed-like organism called the Foamasi? No—the threat is the alien weed and its associated creatures, including the “seaweed” spreading through the installations. The serial is particularly significant because it introduced a gadget that later became one of the Doctor’s most recognisable accessories.

The early Sonic Screwdriver was much less powerful than many later versions. Its function varied, but it generally worked through sound or vibration and could not solve every problem. The Doctor also used it as a welding tool in The Dominators, another 1968 story. The Mind Robber, The Dominators and The War Games are nearby Second Doctor serials, but Fury from the Deep is the established debut.