18 May 1928: birth of John Abineri, who played van Lutyens in Fury from the Deep (1967), Carrington in The Ambassadors of Death (1970), Railton in Death to the Daleks (1974) and Ranquin in The Power of Kroll (1978-79).
ii) broadcast anniversaries
18 May 1968: broadcast of fourth episode of The Wheel in Space. The Cybermen emerge and start to take over the Wheel.
18 May 1974: broadcast of third epsiode of Planet of the Spiders. While exploring the meditation centre, Sarah is transported to Metebelis Three, and the Doctor follows her in the Tardis.
iii) date specified in canon
18 May 1969: setting of much of Paul Leonard's 1999 Eighth Doctor novel, Resurrection Man.