I have a similar query regarding the mast on the US Coast Guard's Island-class cutter, which carries a serious amount of "gadgetry" for such a small ship:
Radars are obvious enough (there are 2 - is one surface scanning and the other air?) as are running lights (the small black cylinders with flared bases) and speakers/sirens, and the double-circle thing on the arm looks like a direction-finder loop. Also not clearly visible in this photo (on the aft side) is the ship's bell and a large spotlight to illuminate the rear deck. But everything else is a mystery to me! I would guess a lot of them are communications-related, including GPS, satellite links etc. Many are under domes (white, grey, and one blue), and this photo shows another large dome on the superstructure roof forward of the windshield - not all of the cutters have this, and I didn't add one to my model.
Doubt there are any USCG experts on this forum, but can anyone familiar with modern ship equipment help me to identify any of the components here?