Gneisenau Radar Capabilities 1941

Post by **José M. Rico** » Tue Mar 01, 2016 8:17 pm

Maybe some of you find this interesting.
On Gneisenau KTB from 23 February 1941.

"1920 hours: Radar device locates Scharnhorst in 356º at 25,000 meters."

At this time both German battleships were operating in the North Atlantic against enemy merchant shipping.

alecsandros · Post by **alecsandros** » Wed Mar 02, 2016 11:00 am

Jose,
It would be interesting to know what type of radar was installed on Gneisenau at the time of the event.
Thanks,

Dave Saxton · Post by **Dave Saxton** » Wed Mar 02, 2016 2:37 pm

It was a FMG(Seetakt)39GgO (later designated retroactively as FuMO22). Gniesenau was equipped with the set from Oct 1939 until it was replaced at Brest France during 1941 by a FuMO27. Also an additional FuMO27 was added aft at that time.

The FMG(Seetakt)39GgO model had the following specs:

Output: 2 kw
PRF: 2,000 or 1,000
Pulse width: 2us
Range accuracy: 100 meters.
Bearing by Max signal

alecsandros · Post by **alecsandros** » Wed Mar 02, 2016 5:02 pm

Thanks you, David,
25km for BB range is pretty good.

Any chance we might learn more about the conditions in which the range was measured ? Was it something normal for such a device ?

Dave Saxton · Post by **Dave Saxton** » Thu Mar 03, 2016 1:16 am

alecsandros wrote:Thanks you, David,
25km for BB range is pretty good.

Any chance we might learn more about the conditions in which the range was measured ? Was it something normal for such a device ?

It was normal for that set. It picked up Renown from the same range in appalling weather and sea conditions during April 1940. Scharnhorst opening fire on Glorious at 26km is not coincidental. Tests pre-war determined it was reliably effective to 25km provided it was foretop mounted.

The newer 1940 models (FuMO27) had at least 4 times more power with a more sensitive receiver, increasing typical range 20% over this set.

alecsandros · Post by **alecsandros** » Thu Mar 03, 2016 9:58 am

Based on those data,
Can we have a reliable estimate of the normal detection range for Fumo27 radars mounted on Bismarck and PRinz Eugen in May 1941 ?
It would be interesting to have estimates (min, max) for each radar set on the ships, depending on it's height of installment...

Dave Saxton · Post by **Dave Saxton** » Thu Mar 03, 2016 3:11 pm

Reliable BB to BB range of foretop mounted FuMO27 was 30km. 20% more than 25km is 30 km. Futhermore, the USN Research Lab's mathematical model will yield a 30km range for a battleship in this context as well. This model will also yield the known maximum reliable ranges of other period radar sets such as Mk3 of 25km and Type 284M of 27km as well, so much confidence can be placed in these results.

30km was the known range of FuMO27 at the time*. Circa 1943 from von Kroge:

The call of the Navy for increasing the range of their Seetakt sets, for both sea surveillance and gun-laying, was more emphatic than that of the Luftwaffe. Their sets which used grid modulated transmitters with two decimeter wave triodes of the type TS6, gave a maximum range of 30km and obviously required increased power.

This was before the development of the large antenna models (FuMO26) and the availability of high power transmitter modules.

The development of the essential triode TS60 had been completed by the start of 1943 so (tube) production could begin. Siemens took over production of the new TS60 because GEMA's tube production for new radars and the supply of replacement tubes was over committed. By mid 1943 the development of the transmitter module Gisela was completed. This extended allowed power on (80cm) to 125 kw or 150 kw. In combination with a partial increase in antenna area where it was possible, this lead to ranges of the ship board sets of up to 60km, according to the size of the target ship. Even from U-boats the increasing of the transmitter power (to FuMO30) gave ranges of 20 km against sea targets, despite the low position of the antenna.

The range of FuMO27 mounted not as high as a foretop would be less of course, perhaps by as much as 30%.

Bismarck's radars were tested before sailing as:

Output power 9kw
PRF 500

FuMO27 circa 1941 had these specs:

Output: 8 kw min.
PRF: 500
Pulse Width; 2 us
Range accuracy: 40 meters
Bearing by Radattel Peilung (phased array scanning)

* Brinkmann stated in the kTB that the foretop EMII device and foretop optics began tracking the Hood at the same time, which was 30km at that time.

alecsandros · Post by **alecsandros** » Thu Mar 03, 2016 3:56 pm

It would be plausible to consider 30km as normal detection range, or maximum reliable detection range for capital ships ?

I'm asking because Hood was coming at almost right angles over Bismarck, thus presenting a smaller surface area to reflect the radar pulses than it would have been if the ship were on a parallel course.

And another matter: we have info from AVKS that the EM-II device was connected to the main battery computers. Any info on the situation of the 3 radars ? Were they all connected, or just the main one ? (foretop)

Dave Saxton · Post by **Dave Saxton** » Thu Mar 03, 2016 4:47 pm

alecsandros wrote:It would be plausible to consider 30km as normal detection range, or maximum reliable detection range for capital ships ?

I'm asking because Hood was coming at almost right angles over Bismarck, thus presenting a smaller surface area to reflect the radar pulses than it would have been if the ship were on a parallel course.

And another matter: we have info from AVKS that the EM-II device was connected to the main battery computers. Any info on the situation of the 3 radars ? Were they all connected, or just the main one ? (foretop)

As I understand it all the radars were linked directly to the computers. This became standard procedure on all German warships. The aft computer on Hipper developed a fault in this connection from the aft radar, so the telephones had to be used, in one example.

circa 1940:

The data wheels (of the new design) were so arranged as to allow selsyns for data transmission. ... This design proved itself and was a feature of subsequent equipment.

Standard radar cross section calculations for ships is cutting across them at a 45* angle, not broadside on. Radar reflectivity is highly dynamic. it is not just down to size and height. Anything can happen.

What is "normal range" and what is the "reliable range for capital ships?" I don't know what you mean here?

alecsandros · Post by **alecsandros** » Thu Mar 03, 2016 7:02 pm

I was thinking of normal range as an average range for multiple conditions and angles at which a capital ship can be identified on the radar.

By maximum range I would imagine the range at which a capital ship could be identified in the best possible conditions...

It's a makeshift terminology... trying to understand the limits of such a device...

Post by **José M. Rico** » Sat Mar 05, 2016 10:22 pm

Also from the same KTB, it is written that at 2000 hours on 16 March, Gneisenau radar device located a battleship of the Nelson Class at 23,800 meters. This was just after sinking the Danish "Chilean Reefer" (1,739 GRT). The battleship was actually the Rodney and Lütjens decided to run away.

Terje Langoy · Post by **Terje Langoy** » Thu Nov 16, 2017 3:28 pm

G'day, all

Are you in possession of Gneisenau's KTB, Jose? Could I make a request whether you have a link to this or even better if the whole log (38 thru 42) is available for download somewhere?

Think I just wet my pants. This sum good shieet

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