Vanguard - no the corrosion crash was at ghent in November 71 - the week I joined BEA - and was the first of eight hull loses the group had in my six years with them.
The corrosion had been known about for two years prior to the pressure dome rupturing - and deemed insignificant.
The Swiss crash was eighteen months later and the result of navigation error.
I seem to remember that the French national grid used the same frequency as one of the ADFs.
As usual fantastic thread guys - thank you.