Thank you for getting back to me, I think you are right about it being ‘hush hush’ at Wivenhoe (and half of what happened in WW2). If you are interested in the history side of it, then I will be happy to share any information with you that I have about an incident at Wivenhoe during the construction of the Mulberry Harbours.
The general story is that during construction they either swapped shifts or there was a tea break where two guys carried on working inside of one of the sections, whilst a swap in shifts or tea break, a crane came along and closed the only exit to the section. I was told that the section was welded shut and then only after it was discovered that two guys were stuck inside.
At the time, it was decided that the section was to remain welded shut because by the time they got in there it would be too late and any use of an acetylene torch would suck any remaining oxygen out and they would not make it anyway. There is a possibility that the Official Secrets Act could have been used to gag everyone involved and who witnessed it. My granddad had been silenced by the Secrets Act either before or after for another incident.