Landmarks No.11

Fury From The Deep.
Love it or loathe it, the Sonic Screwdriver is as much an icon of the show as the TARDIS and the Daleks - and this is the story in which it was introduced.
It was well-known back in the 1970's - even when it wasn't actually employed all that often - but is rarely off screen in the newer stories.
JNT rather over-reacted by having it destroyed (missing out on a merchandising opportunity as well, which was very unlike him). His reason for the axing of the Sonic was sound (pun very much intended) - claiming it made it far too easy for the Doctor to get out of trouble. (Mind you, we would have been spared Peter Davison sitting in a cell for an entire episode of Snakedance).
Lord knows what JNT would have made of more recent series. I have already posted specifically on the Sonic (tying in with my review of this very story) and made my views known therein. I've nothing against it per se, but do dislike:

• Its overuse (generally).
• The ever expanding list of its capabilities.
• Using it like a magic wand.
• The Doctor brandishing it as though it were a weapon.

The story is significant also for a companion departure - Victoria tiring of the hazards of TARDIS life and staying behind with the Harrises.
Sadly, it is Debbie Watling's only story missing in its entirety, save for a few clips.
There is a unique, for the time, TARDIS landing.
It's also a rare example of a story in which none of the characters gets killed.