Hi,
I put here the answer to my last question about the radar:
There are two types of radar you can see on bridge, depending on their wavelength: 3cm (9GHz, X band) and 10cm (3GHz, S band). Only the 3 cm is compulsory because it allows to see the Sart (Search And Rescue Transponder) which are on the liferafts.
Budbud.
*Edit* Maybe this will be more clear:
http://en.wikipedia.org/wiki/Search_and_Rescue_Transponder (http://en.wikipedia.org/wiki/Search_and_Rescue_Transponder)