Instead of debating whether or not Mode S should be in Nimrods, surely the important facts are that;
(a) a fully functional IFF (whatever the appropriate Mk/Mode) is a fundamental safety requirement
(b) senior staffs, up to and including Min(AF), disagree
Here, at para 19,
http://www.iwar.org.uk/news-archive/.../maaszg710.pdf
C-in-C RAFSC disagreed with these senior staffs (although it’s not clear if he knew he was disagreeing with them, as the prior warning of the general problem, and the recommendation that aircraft should be inspected, is not acknowledged in the BOI report).
This appalling attitude, which in this and other cases permitted malfunctioning safety equipment to be fitted to aircraft and offered for Release to Service as fully functional (a criminal act, in my opinion), is what should concern us. I’m sure Nige came across this attitude during his C130 ESF campaign.
All the above is open source/obtained under FOI.