16 April 1936: birth of Derrick Sherwin, script editor of Doctor Who from The Web of Fear to The Mind Robber (in 1968) and producer for The War Games (1969) and Spearhead from Space (1970).
16 April 1954: birth of Antony Root, briefly script editor of Doctor Who in 1981.
ii) broadcast anniversaries
16 April 1966: broadcast of "The Dancing Floor", third episode of the story we now call The Celestial Toymaker. Steven and Dodo must deal with a not-very-threatening kitchen and some rather more threatening dancing dolls.
16 April 2005: broadcast of Aliens of London. A spacecraft crashes into the Thames; the Doctor is among experts on aliens summoned to 10 Downing Street, but all is not as it seems.
iii) date specified in canon
16 April 1746: Battle of Culloden, followed by the events of The Highlanders (1966).