RN Nuclear NIGS ship

Tzoli said:
The Stage 1 3/4 might be the one but the continuation of the same table shows Designs GW70-78 (In Friedman to 81) having explicitly Bristol 1 3/4 missiles
see attachment.
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That actually confirms to me that R.F. is in the same class as Stage 1 3/4, even if it isn't necessarily the same missile - compare GW 70 to GW 61-63, we see the same use of large numbers of single launchers and no 6" guns on a comparably-sized ship. Missile capacity is lower in the later projects, and 'Trackwell' has given way to Type 984 and dedicated illuminators.

My suspicion, and it is just suspicion, is that 'R.F.' was a precursor to Stage 1 3/4, and Trackwell was an envisaged multifunction radar for it, likely more capable than Type 985.
 
How much is the difference between Sage 1 3/4 and the Bloodhound Mk II?
 
Stage 1 and 3/4 was Blue Envoy, a reduced specification from Stage II Green Sparkler.
Range dropped from 200nm and the use of terminal ARH to 150nm and SARH. Both used Command Guidance.

Bloodhound MkII used elements of Blue Envoy to extend range from 50nm to 75nm.
 
RF....reduced firing? Essentially the Bloodhound and Thunderbird type launcher that is slow to load....hence the high number of launchers.
 
Can someone repeat the date for this table?
 
Just open it the designs proposed are in the first line. These designs we are discussing currently are from 1955 June and November. The RF from June, the Bristols from November
 
Hmmmm this is surely before the emergence of phased array radar technology as such.
So both Type 985 and this Trackwell are not necessarily the later options of PAR or FSR (Frequency Scanning Radar).....
 
So I've definitely got something wrong with the quote insert.

Link for example of Frequency Scanning Radar and quite relevant https://www.radartutorial.eu/19.kartei/11.ancient/karte107.en.html

JCF Fuller wrote
With regard to the radar, I have managed to do a bit more digging. The first proposal for a Frequency Scanning Radar is made by ASRE in 1957 and was for a 30ft x 30ft rotating array with a peak transmitter power of 2.5MW. The NIGS arrays were fixed and there would have been four per ship. Based on an ASWE report from 1961, they would have actually been 20ft wide and 15ft high (I was wrong again) with 88 phase changers, 88 frequency scanners and a feed line with 88 outputs. They would have been able to handle a peak power input of 2.5MW. R&D work seems to slow down with abandonment of NIGS but does not completely stop, in 1963 a report is commissioned from someone at Leeds University to look at high power ferromagnetic phase shifters. Later, in 1968 a large (6ft x 6ft based on photos) stacked phase shifting planar array is built and used to test mechanical and electrically controlled ferrite phase shifters. My radar knowledge is weak but the concept seems to have moved on and is now described as Phase Scanning. A peak power upto 4MW is referenced for this design.
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So now I've managed to mess up the quote ?

Frequency Scanning is that as you change frequency so the angle of emitted energy changes.

Phase Scanning is that by delaying the waveform each emitted wave overlaps such that the tangent of them is an angle you can control.
https://www.radartutorial.eu/06.antennas/Phased Array Antenna.en.html#fsa

It's possible that the early Type 985 in the GW59 (relook can't remember number) is this early rotating antenna. As such if it's been scaled down to fit it might drastically cut performance. Rotation would further reduce capability.
Equally this is so early it could actually be a maritime Type 84 set and the Type number reassigned to the later PAR system.......

This further raises the question "what is Trackwell?"
 
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A very interesting discovery.

I have always suspected that Type 985 was separate from the the NSR proposed for NIGS and I think this proves it.

Whatever system GW59 was designed around in 1955 could be considered as the first step on the path to NIGS. It has several similar features;
Multiple single-arm launchers - the Admiralty/ Ministry of Aviation Working Party in 1959 felt that single-arm launchers the right solution and they even discussed having separate high-angle and low-angle launchers, presumably to save power requirements for rapid elevation etc. How this would work in practice I'm not sure without a highly complicated magazine arrangement.

Sea Slug - GW59 only has 28 missiles (3.5 per launcher!) but the missiles seem to be Sea Slug as no other name is provided only non-Sea Slug missiles seemed to be named.

Type 985 - is a search and tracking radar, presumably one radar, sounds very similar in concept to NSR but must have been more than a speculative project in June 1955 as it was assigned a Type number. Two things stand out, the equipment weight for the ship is only 740 tons, some 300 tons lighter than the other GW designs around it and it needs a Type 992 target indication radar. So whatever the Type 985 is, its not a totally standalone system and its not very big. Maybe the Type 985 really is just a digital 984 with guidance added in?

Tonnage - interestingly GW59 is 10,500 tons and yet NIGS was meant to fit on a 6,000 ton hull, this indicates either more miniaturisation of the radar and missile for NIGS or wishful thinking in 1959! But at 540ft long, GW59 is almost County sized.

The other GW ships are interesting too;
GW61 to GW 63 have the mysterious 8 launchers for 32 "R.F." missiles, 1x Trackwell radar. What is interesting is that both ships are far larger than GW59 at 15,000-16,000 tons and 610-640ft long (County was 520ft). No other radar is specified at all, not even a basic Type 974 for navigation. I find this somewhat odd as all the other designs have other radar sensors listed.
Whatever Trackwell is it must be powerful, note that Type 985 on GW985 may be a search/track radar but still needs a Type 992Q for targeting info. Trackwell seems to be able to operate without it. If this is a track/scan radar then it predates the AN/SPG-59 by at least 3 years so cutting edge indeed. At 1,090 tons equipment weight for all 3 GW designs, it seems Trackwell is a large and heavy piece of kit contributing to the weight.

GW70 to GW78 all have the Bristol 1 3/4. Nearly all have 6x T.I.A., 7 of the ships have a dedicated telemetry link, 6 of the ships have a Beacon and oddly GW 72 and GW73 only have the beacon and no T.I.A.! Regardless of the gun armament options, all of these are big and heavy ships of cruiser size.

My money is on the R.F. and Trackwell being a proto-NIGS system, it looks a capable and heavy system and close to the things the 1959 working party were talking about. Whatever 985 is, it doesn't seem quite in the same league. NIGS seems to have followed the Bristol 1 3/4 system and added illuminators too.

My questions are:
Why was Type 985 not used on any other GW ship or with the R.F. missile system and was it really just linked to Sea Slug?
What is the R.F. missile?
What is Trackwell?
What is the T.I.A tracker?
Why where the Navy looking at essentially 3 different systems at the same time (Sea Slug with 985, R.F with Trackwell, Bristol Blue Envoy with 984 & TIAs)

To answer Tzoli's question;
NIGS = New Naval Guided Weapons System
 
I think your answer lies in these workbooks:
Type 985 with RF:
1030/3,
Drawing no.: 6159
Trackwell with RF:
631/7, 622/2, 840/6,
Drawing no.: 6161,62,63
TIA, Beacon and Telemetry with Bristol Missile:
840/6, 631/7,
Drawing no.: 6170,71,72,73,74,75 ,6216,17,20

We should ask our friends who live close to try and check these out! Or in the mean time the entire GW series documents!
 
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So Elliots achieve the first electrically scanned radar in MRS.5.
Prior to that there is electrically scanned in reception Winkle for ECM.

It's possible Trackwell is NSR yes. But this suggests Type 985 might start as replacement of the mechanically scanned Type 984.
The tonnage for 984 was I think 250 tons but this doesn't include 992 or 901 or other guidance systems.

However where is the illuminators for the missiles? Trackwell must be doing that as well, hence my suspicion this is similar to Tychon's SPG59
 
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Hood said:
Why where the Navy looking at essentially 3 different systems at the same time (Sea Slug with 985, R.F with Trackwell, Bristol Blue Envoy with 984 & TIAs)
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My guess there is that the Navy was examining its' options and trying to figure out exactly what it wanted from a cruiser and from its' guided missiles.

We only have the ship side of the debate - I assume that some of the iterations were because there was back-and-forth with the guided weapons people and the radar people about the size, weight and power requirements for their equipment, and what could be accomodated. Some of the studies may have shown that accomodating one requirement was only possible with unacceptable compromises in other areas, helping define the requirements for the combat system and the ship to carry it.
 
Another point.
What we call Track while Scan is essentially what Type 984 and CDS do.

What SPG59 does is Search, Track and Illuminate and does it effectively simultaneously.

While what we've read here about NSR and NIGS is the Illumination function is separate from a combined search and track set.

TIA could stand for Targe Illumination Array
As Type 86 Firelight and Type 87 Scorpion sets are actually a combination of tracking illuminators and height finding sets. Coupled ECM assessment equipment.
 
I've made a modification to my drawing of the NIGS Scheme 16 Nuclear DDG.
Here is the Scheme 17 the COSAG propulsion version:
RN-NIGS-Ship-17.png


not much change just made some decks more round and of course added the funnels.
 
I would presume that Freidman found them at the Brass Foundry, Greenwich. That is where DNC materials are generally archived.
 
Friedman's books refer so often to things that would be interesting to know more about.
It would almost be worth taking the what if references from various Friedman books and listing them in a thread here so people can follow them up.
 
uk 75 said:
It would almost be worth taking the what if references from various Friedman books and listing them in a thread here so people can follow them up.
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Would be a big job but might be fruitful, I doubt he lists every source but as someone else said the other day, his footnotes/endnotes are often more interesting in terms of details than the main text. Indeed they probably form about a quarter of his latest cold war subs book!
 
Yes he often states more detailed info in the footnotes or sometimes under drawings/pictures. Though I would be very happy if he would state what kind of lenght data a peculiar design had. It is often very difficult to determine if he states between perpendicular, waterline or overall length...
But the era sometimes help as WW1/pre-WW1 the dominant length data stated was pp, after WW1 and before Cold War the waterline length and for Cold War/Modern ships this changes to overall lenght.
 
The section @Tzoli quoted from Friedman's British Destroyers and Frigates of the Post War Era is largely referenced out to constructors notebooks which I understand are held at the National Maritime Museum at Greenwich. The only specific notebook he references is 1073/3. In that passage Friedman has the work on NIGS ships starting, at DNC's behest, in June 1959 which lines up nicely with the period during which the NIGS working party was active. The adapted Hampshire class drawings that were included in the final report of the NIGS working party were probably the end result of all that work but that is speculation by me until I see the constructors notebooks.

In general, ship images at Kew are rare, they do come up from time to time but usually as part of other reports. Frustratingly, many documents included in files refer to artists impressions or diagrams that have not been preserved within the file.

The Royal Navy's interest in nuclear propulsion for surface ships is another under appreciated and under studied part of the 1950s and early 1960s history. A lot of study work was undertaken looking at the advantages, disadvantages, appropriate reactor technologies, propulsion system configurations, etc.
 
Friedman states TIA is a 4ft tracker Illuminator.
 
Just seen a copy of Warship 2022 and the article on postwar RN radars.

Only bare snippets on Type 985, it was a study that ran 1956-60 and seemed to cover all the various approaches (frequency scanning, arrays, etc.) but it sounds like little got done before cancellation. But at least it covers dates to give us the timescale.

There was another requirement after this which 3 UK companies tendered for but it went to Broomstick.
The article also says that work on active arrays in the UK did not begin until 1977.
 
However....

SLA3
Frequency Scanning Phased Array Radar.
Precision Approach radar used since 1966.

SLA 3 - Radartutorial

www.radartutorial.eu www.radartutorial.eu

Which curiously shows X-band was achievable in that time.
 
I would put a slightly different spin on it. The ASRE, later ASWE, undertook a broad range of R&D work to explore various technologies. However, I can detect no formal programme for a post-984 radar until the late 1950s, I suspect it emerged out of the NIGS studies and 985 was simply a reserved designation for whatever a next-generation aircraft direction radar might be.

The naval Blue Envoy studies ended with the cancellation of the missile so never reached a full conclusion, but in 1956 the assumption was it would be paired with the Type 984, probably in modified form. There is an interesting proposal for a large rotating frequency scanning array from 1957 but I've not been able to tie it to any specific project. From then, through to at least the late 1960s, ASWE was very interested in Frequency Scanning radars.

My own opinion, and its nothing more than that, is that even if Blue Envoy hadn't been cancelled the RN would have eventually dropped it anyway as it was wholly unsuitable for ship fitting. The result would have been NIGS as we know it. Even if the RN had continued with Blue Envoy, in a world where it wasn't cancelled, I think its inevitable it would ultimately have been paired with a Frequency Scanning set.

1977 seems reasonable for starting work on AESA sets, the first naval AESA was the Japanese OPS-24 that was installed on a destroyer in 1988. Western industry was fairly dismissive of it at the time but that may have been sour grapes. Either way, whilst the Japanese system was first I don't think the UK effort was particularly far behind, if at all, in terms of actual technology. The time to get the MESAR research to sea, and the subsequent poor utilisation of it across the fleet, is a different matter (and well off-topic).
 
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Now that I have the Peter Marland article in front of me a few additional details.

Type 984 began as 'Project Postal' in 1947, designed early 1950s and a complete development model completed in 1955, installed in HMS Victorious in 1958. Marland puts the 984 with CDS and DPT as being about 5 years ahead of the USN.

Type 985 - a second generation set, experimental work 1956-60. Concepts studied included "frequency scanning, travelling wave tubes, phased arrays, multiple pulse-forming circuitry, and other techniques." Prior to the project definition phase it was replaced by Project 988 'Broomstick' in 1960 (itself cancelled in 1968).

NSR.7938 - Type 1015 for a new long-range radar [note that this designation was in the IFF numbering sequence for some unknown reason! It should probably have been 989]. Dual frequency UHF (430/600MHz) with back-to-back or wrap-around antennae to remove need for a masthead location. Studies included 'Broomstick', SPS-52 and three UK designs from EMI, Plessey and Marconi. Later studies included a modernised Type 965, SPS-40B, LW-08 and Selenia SPS-68. Cancelled in late 1971.
[The ASWE report I found at Kew - ASWE Laboratory Report XRA-63-5 A Study of a Proposed Radar System Employing Within-Pulse Electronic Scanning over 360° - dated August 1963 using a cylindrical array must be connected with this.]

There is no mention of 'Trackwell'. There is mention in the article of a Type 983/983 replacement for fighter direction in 1953, described as a "mini-984" with a V-beam. Since 'Trackwell' doesn't seem to need a 992Q TI radar its possible its an outgrowth of this 'mini-984' concept?

In all there seems to be a sense of confusion and overlapping work and the more we dig, the more we find a lack of concrete developments. It feels like when NIGS/985 were canned in 1960 in favour of newer missile and radar technology, that they were perhaps another 5-10 years away from operation. They were becoming superseded but certainly the overall radar development picture (see here for more on the Marland article) is one of downgrading, chopping, cancellation and losing the lead to US, Dutch and even Italian competitors. There does seem to have been a mismatch between the systems and the ships, really there should have been integrated development.
 
So according to these new findings, the Type 985's one version is the equivalent of the SPS-32/33 (Phased Arrays). What was the other types in USN service? Frequency scanning, travelling wave tubes and multiple pulse forming?

SPS-48 seems to be a frequency scanning type.
 
Almost all 3D radars in the USN are of the Frequency Scanning type, often refered to as "FRESCAN". SPS-26 was the first, developed into SPS-39, then SPS-52. SPS-48 replaced SPS-52 and is considered the ultimate USN FRESCAN radar. IIRC Broomstick used technology similar to the USN FRESCAN radars on it's 3D antenna's.
 
On a theoretical side one could replace the mechanical movement of feed horns in the Type 984 with electrical scan. But I'm unsure it's compatible with the 'lense'
It's certainly possible to replicate 984 in higher bands even to X-band accepting other compromises this could become very precise.

It's also clear the design could be scaled down, accepting greater limitations on range. I do like the idea.

But Trackwell seems to be doing everything like SPG59.
 
Anybody intend to visit the archives for more info on the GWS and NIGS designs?
We have the data tables for the GWS but we lack the important text pages describing them and their equipment.
 
Pardon me, archive binging again!

Grey Havoc said:
Speaking of USN nuclear powered ships, given the timeframe do you think it's possible a successful NIGS design might have ended up using a couple of the USN's D2G reactors?
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Possibly. The S5W that the UK got ahold of is 15,000hp, the D2G is twice that.

I'm not sure how scalable the S5W/PWR1 design is, and I'm not sure the answer is something that we could put here.

However, note that a nuclear powered cruiser or destroyer is going to be 9,000-10,000 tons. D2G is roughly 1400 tons of reactor and systems!


JFC Fuller said:
Just a quick note on studied RN nuclear propulsion plants of the time.

The Director of General Engineering studied a configuration consisting of a 20,000SHP plus a 20,000SHP pressure fired boiler, there was a second study with 30,000SHP at each of the two stages.
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CONAS seems such an odd design.

The bigger study is D2G power levels out of the reactor. It looks like the C1W for the Long Beach is 40k hp.

And again, the minimum size for a nuclear powered surface ship seems to run about 9000 tons.


Hood said:
It seems odd that the work on the NIGS studies was not used for the SIGS frigate, they must have known that the NIGS ships were the optimum size for air-defence ships and yet they went back to sqaure one and came right back to a 7,000 ton destroyer.
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I have a sneaking suspicion that the SIGS folks were told "7000 tons is too big, do another study and find a smaller size (= cheaper) ship!"



uk 75 said:
The Talos system gave the USN amazing long range reach, as demonstrated over Vietnam, but was only available on one or sometimes two platforms in a task force.
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The Talos ship also tended to carry the Air Defense Flag, the Commodore or 1-star admiral in charge of the entire escort group.

At the time, there weren't a huge number of missiles in any given attack on the carrier group (only one missile per bomber). This meant that the Talos ship could sit next to the carrier as goalkeeper and still put missiles out onto the incoming, while the Terrier/Tartar ships were probably 30 miles away and able to shoot at about the same time.



Hood said:
The Fourth Meeting discussed possible launchers and estimated ship sizes.
6,000 tons was the desired size of the ship, with 40-50 missiles. No studies had been made at that time, but it was roughly working out at 8,000 tons and 30ft longer than County at that stage. If no guns were fitted then 2 launchers might fit on 6-7,000 tons.
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There they go again, trying to stuff 10lbs of stuff into a 1lb can...



uk 75 said:
We know how impressive Talos could be at downing jets at extreme range. It also had a useful surface to surface capability according to one source.
But it was a deadend and by 1980 had gone to be replaced by Standard. Seadart compared favourably at first with early Standards. But Standard continued to evolve.
Would the taxpayer have been better served if CF299 and Aster had gone the way of NIGs. Or could we have done more with Seadart?
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You could have done a LOT more with Sea Dart.

As electronics got smaller, redesign the missile body to fit more fuel in, maybe use a larger booster, and probably a larger warhead. FFS, Sidewinder has a warhead nearly that big!

Talos went through 2 airframe redesigns while in service. First to increase range, second to a unified airframe so that ships could just store a few nuclear warheads instead of complete missiles and swap warheads as needed.



Hood said:
I have done a very crude estimation to see if indeed the launcher drawings matched a conversion of a County class hull.
The attached is a crude mashup of my scaled NIGS launcher and magazine to a cross section of the County hull with the deck lines and features shown matched up as close as possible to the plans.

What is surprising is perhaps the height of the NIGS launchers, they are quite high but perhaps not impossibly so for topweight concerns.
The forward launcher means the removal of the B turret (I suspect A would go too) and the complete replacement of the forward superstructure and bridge. Of course the plan drawing only shows us the forward angled face for the search radar. I suspect there would be one block holding all four arrays. I think that would fit but the aft array would be rather blocked by the forward funnel which I suspect would be removed, perhaps to be put into a midships mack to hold the usual surface search and navigation sets. Also, where would the bridge go? Below the angled radar block - which would be very low and probably poor views given the NIGS launcher right in front of it, especially given the missile blast problems - or on top of the search radars which would be very high indeed - effectively at foremast level!
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Ticos and Burkes put the bridge above the antennas. And yes, the bridge on a Tico is something like 110ft up!



uk 75 said:
Did the RN really need a TALOS analogue? Probably rightly it decided it didnt.
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Personally disagree. Once the threat was Mach 3 missiles, you need a long range SAM to intercept with a long range radar to go with.

Now that I think about it, that's probably the reason the Constellation-class FFGs got Aegis and SPY6s.


uk 75 said:
If I were to design a NIGS ship in 1958 it would look like ALBANY or LONG BEACH, though as the RN never came close to designing a nuclear surface combatant an ALBANY style 1957 cruiser revamp, Macks and all, would be my bet
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Agreed that something like the Albany is highly likely.



zen said:
Well when we look at the comparison between a Cruiser with twin Sea Dart Systems and the Type 82 DDG, it seems that for 50% more cost per ship you get more than twice (200%) more capability.
One might say that constrained ship size results in constrained ship life and constrained ship utility.
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Exactly.



Tzoli said:
Here is my interpretation of the Scheme 16 NIGS DDGN design:
www.deviantart.com

RN Nuclear NIGS Missile Ship Scheme 16 by Tzoli on DeviantArt

www.deviantart.com www.deviantart.com
ddqhf1l-7cada0ff-6bb3-4547-bbdb-a9a1c49af21d.png


The design had the following characteristics:
Dimensions: 170.69m (oa) x 18,29 x 5,67m
Displacement: 8500tons (standard)
Engines: 60.000shp, Westinghouse D1G or Rolls-Royce PWR1 Nuclear Reactors, 2 shafts
Range: Unlimited
Speed: Unknown probably around 59km/h (32knots)
Armaments:
2x2 NIGS SAM
3x4 GWS.21 Seacat SAM
2x1 40mm/56 QF Mk VIII AA Guns
2x Westland Wessex Helicopters
Sensors:
3x Type 903 Fire-control Radar, one for each MRS.3 director
1x Type 978 Surface Search / Navigation radar
4x Type 985 Tracking and Search radars
4x NIGS Illuminator Radars
1x Type 992 Air/Surface Search Radar
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Very nice! As a side note, the PWR1 reactor is half the power needed. This would probably get something called a PWR2 that has little-to-nothing to do with the modern PWR2 in the Vanguard SSBNs or Astute class. The modern PWR2 is a bit under powered for what you're saying, only 27,500hp instead of the D1G's 30,000hp.
 
Grey Havoc said:
That and dear old McNamara.
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Right, because the Beast of the East was absurdly expensive to run, but also too expensive to refit with 2x big reactors like Nimitz. (as far as I know, the USN has only removed reactors from one ship while still in service, and that was the 575 Seawolf when they scrapped the molten sodium reactor idea. Too hard to keep molten sodium out of the water side of the steam generators!)

Each reactor needs a minimum of ~9 dudes operating it, times however many watches the engineers get split into on a carrier. I'll assume 4 watch sections, since that's about how many dudes the subs tended to carry, counting new bodies and seniors. 8*9*4 is 288 bodies. 2*9*4 is 72. Saving 200+ crew numbers.

Then there's all the pumps and stuff to maintain. Any given reactor has reactor coolant pumps that circulate primary coolant, at least one per loop on the reactor. Then you have the steam generators, one per loop, that get heat out of Primary coolant and into the secondary loop as steam. There's also Condensate pumps and Main Seawater pumps, at least one per loop. Plus however many main engines (I think the Enterprise ran 8x while Nimitz runs 4x at twice the horsepower per). One set of reduction gears per shaft, so those aren't any less with fewer reactors feeding them.

Two reactors feeding 4 shafts means dual loops per reactor; but you still save 6x reactors, at least 6x RCPs, 4x Steam Generators, 4x Condensate Pumps, 4x MSW pumps, and 4x main engines to maintain.

========================

So I really don't think that 4x S5W/PWR1s driving a cruiser or carrier is a good idea. It'd take a lot more crew to man and a lot more work to maintain all the things. And the RN is a lot more sensitive to that side of the equation than the USN is. Note that it took until the Ford class to redesign a new set of reactors that don't have as many pumps and take less crew to operate.
 
I've contacted an Independent Researcher who is likely able to acquire documents from the Naval archives, among other on the NIGS warship designs and likely on the missile. Currently the [ADM 220/2179] document. But if anybody knows other document IDs related to the NIGS and associated warships please share it with me so the researcher can get access to those as well on my behalf!
 
RE: CONAS.

I can see a couple of different ways to do CONAS. How was the RN planning to do this?

IIRC, the Soviets used reactors with oil-fired superheaters. The other ways I could think of would be separate boilers using the same turbines and separate boilers and turbines. A sort of hybrid between the last two would be to use an extra high pressure, supplied high pressure steam from fossil-fired boilers, exhausting into the HPT for the reactor.

I suspect, though, CONAG would be easier.
 
1635yankee said:
IIRC, the Soviets used reactors with oil-fired superheaters. The other ways I could think of would be separate boilers using the same turbines and separate boilers and turbines. A sort of hybrid between the last two would be to use an extra high pressure, supplied high pressure steam from fossil-fired boilers, exhausting into the HPT for the reactor.
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Oil-fired superheat lets you run superheated steam, which PWRs can't do, so gets you theoretically better performance from your neutrons but you're dependent on having oil fuel for good performance. It does seem to be what the Soviets did, and is probably the best way to do CONAS.

Separate boilers feeding the same turbines requires that the turbines run on saturated steam, which is an inefficient way to burn oil fuel and not great for turbines. Nuclear plants deal with this because they have to, and because fuel efficiency is less of a concern for them. AFAIK this is how the West thought the Soviet CONAS plants worked, but it seems to just be bad.

Entirely separate oil-fired and nuclear plants geared onto the same shaft adds a whole bunch of weight and complexity, but makes the plant design and operation effectively independent. At this point, you've just got an oil-fired boost plant. CONAG is a much lighter way to do that.

If the RN was talking about a 20,000 shp nuclear plant and a 20,000 shp steam plant, I suspect they were thinking in terms of the third option.
 
Yellow Palace said:
Oil-fired superheat lets you run superheated steam, which PWRs can't do, so gets you theoretically better performance from your neutrons but you're dependent on having oil fuel for good performance. It does seem to be what the Soviets did, and is probably the best way to do CONAS.

Separate boilers feeding the same turbines requires that the turbines run on saturated steam, which is an inefficient way to burn oil fuel and not great for turbines. Nuclear plants deal with this because they have to, and because fuel efficiency is less of a concern for them. AFAIK this is how the West thought the Soviet CONAS plants worked, but it seems to just be bad.

Entirely separate oil-fired and nuclear plants geared onto the same shaft adds a whole bunch of weight and complexity, but makes the plant design and operation effectively independent. At this point, you've just got an oil-fired boost plant. CONAG is a much lighter way to do that.

If the RN was talking about a 20,000 shp nuclear plant and a 20,000 shp steam plant, I suspect they were thinking in terms of the third option.
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I can't say exactly how the 50/50 CONAS plant would have worked but I am certain that it was an option considered only briefly under a much wider nuclear propulsion study. The study that was ongoing at the time ultimately concluded that CONAG would be the optimum solution for a 75,000 SHP plant for guided missile destroyers. Specifically, a single reactor delivering 60,000 SHP and two 7,500 SHP G6 gas turbines to provide emergency power, rapid start-up and boost from 80% power to 100% power. The logic was:
  1. The nuclear part of the system was heavy, anything to make it lighter was good, e.g. having alternative emergency power meant only one reactor was needed and using the Gas Turbines for boost meant that the single reactor could be smaller and lighter
  2. The study assumed the ship had a double bottom, the double bottom would have to be filled with liquid anyway so that liquid may as well be fuel
  3. Like conventional boilers, nuclear reactors were slow to raise steam, adding gas turbines solved for this, allowing the ship to get underway faster
As you point out, PWRs couldn't produce superheated steam. There was a view that a gas cooled reactor, specifically a CO2 cooled, graphite moderated reactor, would offer a lighter weight solution that could produce steam comparable to modern oil fired boilers. This would require more work but might be a practical proposition in the future. The added advantage of the gas cooled reactor was that further development would support a path to a gas cooled reactor connected directly to a closed cycle gas turbine, that being considered the ultimate power reactor at the time. The downside was the need for much greater pumping power to circulate the coolant than was necessary for a PWR.

Note that this was all 1956-58.
 
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