The ICU designation does not say much about what these carry, nor what kinds of incidents they are supposed to respond to, nor why? Some French and German tactical support vehicles, trailers and pods suffer from incomprehensible acronyms too, but these London trucks are pretty mysterious as well!
I suppose you could argue that ANY fire truck is a vehicle which responds to incidents, after all...
Rob, the what-you-refer-to-as "mysterious" lack of detail is a deliberate molly-coddling ploy by the authorities to play down the role of these and other vehicles purchased under the "New Dimensions" scheme, post-9/11. The DIM units have no writing on them whatsoever, again done deliberately. The thinking behind this is not to panic the public unnecessarily.
I suppose you could argue that ANY fire truck is a vehicle which responds to incidents, after all...
Ed: best summary is www.romar.org.uk/page129.html
Added by Rob Johnson on 10 January 2021.