Of course with the internet means they code words are widely known (they were also named on The Crown) - and indeed trending on twitter, which is amusing given how some documentation still says they are super secret. The information can't be easily kept underwraps now as the chance of someone scooping it on twitter increases with the number of people aware of it and the time taken, I suspect there's only a few minutes between the palace announcing it to bbc/sky/itn and the embargo time - certainly BBC didn't have enough time to get Huw Edwards in for example (he's in now)
Other bridges includ(ed)
Menai (Charles - Price of Wales, Menai Bridge is from Bangor to Anglesey)
Tay (Queen Mother, near balmoral which I think was her ancestral home)
London (Queen, London being the captial)
Forth being the bridge at Edinburgh, so makes sense for the Duke of Edinburh)
Not sure if William has one, maybe it would be the River Cam.
The specific details however aren't public knowlege, with various secrecy levels, and there are various different plans depending on the situation (what happens if the queen was on a plane that crashed for example, or what if Charles died in an avalanche in Austria), and plans of course are constantly changing (what happens if there's a massive pandemic which means people can't congregate in their millions to pay respects as they did with Diana, what happens if the news is leaked on twitter before coordinated official announcement)
https://www.theguardian.com/uk-news/2017/mar/16/what-happens...
Philip had the title of Duke of Edinburgh and the Forth Bridge is a large bridge near Edinburgh.
https://en.wikipedia.org/wiki/Operation_London_Bridge
https://en.wikipedia.org/wiki/Forth_Bridge
Edinburgh sits on the south side of the Firth of Forth:
https://idioms.thefreedictionary.com/be+like+painting+the+Fo...
QE is - Operation London Bridge
Usually when there are preperations for a future event to hide the markers of what it is there are code names.
Operations for preparing the necessary for the deaths of heads of state are typically named bridges.
The Queens death is (or was) Operation London Bridge.