Hi Lars, I hope this slightly long winded reply can settle a few things.

Quote from the book ‘Shipboard Antennas’ 2nd edition, 1986, ISBN 0890062110, by Preston Law Jr, The Former head of The topside Electromagnetics Design Branch of the Naval Sea Systems Command. (in other words, pretty much the authority on US Naval radar systems)

Ch4 3.14 pg 318
“Radar set AN/SPQ-9A is part of the shipboard MK86 Gun Fire Control System as its prime sensor of range and azimuth data on surface and low altitude targets. The MK86 GFCS, used to control lightweight, rapid fire five-inch/54mm guns, employs AN/SPG-60 monopulse radar for air track and the SPQ-9 for surface search capability.”

From ‘Naval Radar’ 1981, ISBN 0870219677, by Norman Friedman

Pg 181
“SPQ-9 is intended to operate out to 20nm with a minimum range of 150yds. There are reportedly two versions: one for surface search and very limited (2000ft) air search, and the other, with integral IFF, for air search up to an elevation of 25deg. Only the surface version is dome-enclosed.”

‘The Naval Institute Guide to World Naval Systems’ – 5th edition, 2006 ISBN 9781557502629, by Norman Friedman

Pg 322/323
“SPQ-9B is a new radar developed by NRL. It uses a modified SPQ-9 antenna and is intended specifically to detect incoming, low flying, anti-ship missiles. Compared with SPQ-9, -9B uses a slightly modified antenna pedestal, a slightly enlarged Radome, and completely new belowdecks elements. However, the operator interface for surface gunnery has remained unchanged. Existing SPQ-9s may be modified to -9B by ORDALT. On board ships with Sea Sparrow, SPQ-9B is replacing TAS Mk23.” “This radar is to be used for gun control on board the Project Deepwater national security cutters (USCG ships)”
(Ordnance Alteration (ORDALT) instructions provide naval activities with all of the information necessary to affect the alteration of naval ordnance weapons, weapon systems, computer programs, and Equipment.)

Important Points:
- A Surface Search Radar can be used for Air Search. (Up to a certain height depending on how it’s antenna is angled)
- A Surface Search Fire Control Radar provides data. That data can be sent to several different systems, including gun, missile, close in defense, etc.)
- The 9B upgrade added the antiship missile detection and Sea Sparrow control to the 9A, it didn’t replace the 9A.
- It is clear that the 9A was a Surface Search radar for the MK86 GFCS, therefore, the 9B still retains that role.
- The SPS-73(V)18 has a very important improvement over other radars. A software upgrade can be written to add new capabilities. For instance, software can be written to add weapons control. It can be written to add antiship missile detection. It can be written to add air search. That’s why it’s so versatile. Just because it doesn’t have all these abilities yet, doesn’t mean it won’t get them.

Regards,
Darren