Shipbucket

There is a large cylindrical structure on both vessels that the MR-750 Fregat radara rests on. Is this a separate system or simply just an odd design to the mast?

Its a Rezistor 4K model fligth controll radar

Is that a conventional primary radar or TACAN equivalent? I've seen it labelled as the latter in CW-era publications.

- RP1

It should be conventional radar AFAIK, intended to monitor the fligth activities of the ship, where as the Mars-passat and Fregat are for more general air surveilance.

That makes much more sense. It always seemed impossibly large to be a TACAN equivalent.

"It always seemed impossibly large to be a TACAN equivalent."

Not really. Land based Tacan arrays can be huge. Add in some maintenance space and the datalink that it is credited with and it would easily occupy that space. Some Googling for RSBN - the Soviet equivalent of TACAN shows semi-mobile land systems of not entirely dissimilar dimensions.

RP1

Well, I'd scarcely be able to think of any single shipboard component that couldn't be made more efficient, more reliable, better performing, etc. with an unlimited weight and volume budget. If I might rephrase a fairly off-the-cuff comment, the giant drum always seemed somewhat implausible to me under the NATO TACAN paradigm. A duplex-communication system is always going to scale more slowly than a primary radar (something like R^2 rather than something like R^4), and one can be sure that a steep price was paid to put such a large object so high in the superstructure. Surely this price must have bought an important capability, one that could not be nearly achieved by something much smaller (like the ubiquitous URN-3 (PDF warning) of the 1950s). And even then, by such an early date as 1950 I can't imagine that very much equipment would need to be collocated with the antennas, whatever those might have been. As for antenna size, the system seems to dwarf even a civilian VOR/DME station, which has far less demanding size limitations. It's difficult to imagine why a secondary radar antenna should ever need to be so big at any reasonable frequency.

Now, I don't mean to suggest that the giant drum doesn't perform a similar mission to what we know as TACAN, but it does make a great deal more sense to me that it incorporates, in part, a primary radar for flight control.