Use of Seetakt on German ships for FLAK direction.

[Siegfried]

In Louis Browns "Radar History of WW2" he makes mention of the Kriegsmarine integrating Seetakt with the ships FLAK fire control system sometime after Bismark's loss. One can certainly immagine an early Seetakt detecting an aircraft and queing an optical director onto a target as well as providing range data to FLAK predictor even though their bearing resolution was inadaquet for accurate gunlaying. Since the radars were mounted on the main directors and the FLAK directors were seperate how was this accomplished? Were there selsyn transmitters that could slave the main directors, on which the radars were mounted, to the FLAK directors? Were there subsidiary osciliscopes in the FLAK directors so that range could be injected directly into the FLAK director computers (as they were for Wurzburg D) or could the main directors accomplish FLAK direction on their own. Later versions of the Seetakt series such as FuMO 24,25 and 26 had a type of fine direction finding similar to lobe switching often quoted as being accurate to 0.3 degrees and 0.25 for FuMO 26.

This degree of accuracy is usefull enough for FLAK direction bar the lack of height finding abillity. However Harry con Krogge's history of the GEMA company (the makers of Seetakt and Freya radars and German naval sonar) mentions that 58 height finding antena for ships were delivered to the navy. I've never been sure as to whether to interpret this as meaning that "Flakleit-g" a nodding antena for height determination had been added (as some photographs of prince eugen show) or whether a phased array beam steering system for height finding had been added. This is certainly conceivable as the GEMA company's land based Wasserman radars had exactly this facility.

Is it possible that these larger German ships had full radar directed anti aircraft gunlaying capabillity?

[Dave Saxton]

The data circuits for the surface firecontrol could access the flak firecontrol circuits. Thus radar data could be transmitted via selsyns directly to the flak fire control by-passing the optical flak directors. So this statement is more or less correct:

or could the main directors accomplish FLAK direction on their own.

However, German optical surface firecontrol for day light operations did not use combination rangefinder-directors like other navies. The optical range finders and the optical directors were seperate instruments divorced from each other.

Later versions of the Seetakt series such as FuMO 24,25 and 26 had a type of fine direction finding similar to lobe switching often quoted as being accurate to 0.3 degrees and 0.25 for FuMO 26.

This was a type of lobe switching introduced in 1940, but as far as is known not used on major warships until the fall of 1941, first on the Tirpitz. The type of lobe switching was known "radattel peilung". In this type of lobe switching the receiving antenna dipoles (only) were set up in a phased array scanning loop by a 1/2 wave delay line and a motor driven contact was circulated around the 1/2 wave delay line. The contact made a raddling sound when in use, hence the nick name. The pip on the bearing indicator scope took the form of a saddle shape and with the notch of the pip centered right in the middle of the null mark in the middle of the scope; the antenna was aimed directly at the target within a directional accuracy of 0.1*. 0.3-0.25* accuracy is incorrect. The bearing accuracy attainable with radattel peilung was 0.1* If the target wandered off line, the pip on the indicator moved accordingly. It was just a matter of adding another crt indicator module to the radar for the vertical lobe switching indication.

Flakleit-G (literally translated as Flak directing -GEMA -g wave length) used the "owls ears" attachments to the antenna as seen on the Prinz Eugen in 1942 and early 1943. These owls ears antenna additions were for locating the aircraft on the vertical axis. One owl ear was for transmission and the other with radattel peilung lobe switching was for receiving. Thus radattel peilung could be used on both the vertical and the horizontal axis providing full blind fire capability against aircraft as well as surface targets. In 1943 a new model radar superseded both FuMO27 and Flakleit-G on warships. This was known under the 1944 designation system as FuMO26 with a huge 6.5 meters x 3.2 meters common mode antenna. This antenna could employ vertical lobe switching without the use of owls ears attachments because it had four rows of dipoles. The common mode technology could also be retrofitted to existing radar sets/antennas bringing all available dipoles into service for both send and recieve. Hence some existing Flakleit -G sets only needed one owl ear antenna attachment late war.

Without vertical lobe switching, the radars with antennas mounted to the rangefinders, could be used to track aircraft; providing accurate range and bearing, and the optical flak directors only need provide elevation data. In some film footage of Tirpitz during 1942, the foretop rangefinder mounted radar can be seen tracking a fast moving Luftwaffe aircraft from the port side across the bows to starboard in a radial arc. Even prior to the employment of horizontal lobe switching the radars could be used to provide accurate range data to the flak control computor circuits.

[Siegfried]

Thankyou for this information Mr Saxton. Might I ask what kind of material on this topic you have accumulated? It is unique and has the potential to rewrite parts of WW2 naval history. I am eagerly awaiting a book from you.

The poor perceived FLAK fire control attributed to the Kriegsmarine has never made sense when compared to the Luftwaffe capabilities: Wurzburg-D had conical scan with syncho injection of range data into the Lamda predictor in early 1941 according to Trenkle. Connical scan had come in with Wurzburg-C even earlier (it lacked range resolution and the synchro links to the predictor). It would be difficult to believe that the Kriegsmarine would not seek a way to place Wurzburg like gun laying capabilties onto their ships and so rather than use higher frequencies and smaller seperate anteans they found a way to do so via Seetakt. I suspect FuMO 26 lacked the abillity to track targets directly overhead, hence the Wurzburg-D (or Mannheim) set added on to Tirpitz's rear deck.

The Luftwaffe FuMG 64 "Mannheim" radar (konwn as FuMO 221 when used by German Navy Shore Defense) had a 3m dish like Wurzburg (and often confused with Wurzburg) was about twice as accurate as Wurzburg (0.15-0.2) degrees due to the indication of deviation of the target on guages rather than just osciliscopes and due to a much better range circuit (6m in some cases). The 2nd issue of this radar even had track locking for the range gate.

The "FuMO 231 Euklid" was to be the Kiegamarine's FLAK laying rada for destroyer sizes ships, it seems to have been a half scale FuMO 221 Manheim" with 1.5m antena and 27cm instead of 54cm wavelength. These radars used LD6 or LD7 disk triodes that were the fruits Germany's rather low priority microwave program.

[Dave Saxton]

The book is coming along well, although incorporating and accessing many high quality photos has proven difficult. The OKM’s records of the secret KM symposium on radar during March 1944 has been most useful, among others.

Regarding Euklid, although the GEMA radar could do the job, the antenna was too large for many applications, and conical scanning was certainly the better concept for aircraft tracking and targeting. Wuerzburg’s 3 meter dish was also larger than desired. The KM wanted a navalized Wuerzburg with only 1.5 meter dish along with a new highly advanced director, the M42, to go with it. The compact antenna of course required a shorter wave length. The need for a shorter wave length to go along with more compact antennas in their Air Intercept radar research was also the reason the British originally sought microwave radar. Telefunken used disk triodes, while GEC used strapped magnetrons.

In 1942, Karl Rottgardt the appointed head of Telefunken ordered R&D into microwave radar stopped. The KM saved Euklid by having the Telefunken engineers continue under the authority of the NVK. Euklid and the M42 director had almost completed development and was almost ready for sea trials. The discovery of the H2S radar at Rotterdam had a delaying effect upon the deployment of Euklid. Telefunken R&D then fell under the overlapping authority of the Rotterdam Commission and its priorities. They spent most of 1943 seeing if the British 9cm technology could or should be used by Euklid among other projects. Euklid performed better in trials operating at 27cm than it did at 9cm using the British strapped magnetron. But they also discovered that the strapped magnetron produced more output power than the disk triodes could at 9cm. By 44 it was decided to go ahead with Euklid at 27cm. Then Euklid was tested at 3cm and it performed very well (conical scan with the focused beam of 3cm off of a 1.5 meter dish). It was planned to have Euklid (with 3cm options) operational with the fleet by April 1945, but of course that last year didn’t go that well for the Germans.

[Siegfried]

One of several questions for me now is the true state of Bismarck radar integration with the FLAK system. The four heavy FLAK directors did seem to have 4m base range finders. The aft pair of FLAK directors I believe were on older 2D stabilised system as the full 3D system had been given to the Soviet Union as part of co-operation agreements that were taken very seriously.

When Bismark was attacked by the swordfish torpedo bombers she seemed unable to do anything but make the bombers task difficult and dangerous though she only managed to inflict shrapnel damage to the aircraft. Visibility conditions were probably terrible given the time of the attacks given weather and twilight. (Visibility is another question for me)

How did the two factors influence this insufficient performance?

At the minimum the FUMO 23 should have been able to locate aircraft and direct optical directors to it or provide accurate ranging data to the optical directors.

The AVKS 700 report (available on this site I believe) by von Goetz also mentions over crowding and insufficient space in the FLAK control rooms and several problems but its also clear that there was some integration of FLAK with radar (referred to as EM-II) or range finding instrument II.

Of course the Bismarck’s radars were likely out of action due to the action with Norfolk.

It may be that the loss of the radars effected Bismarck’s defence considerably.

Regarding the abandonment of a strong effort towards the development higher frequency radars. In hindsight this was a severely incorrect decision though it seems to have been part of a manpower issue it is said that many of the researchers ended up drafted into the military and had to be recalled when the British H2S magnetron was recovered from a shot down Stirling bomber. Had the program continued I sspect they Germans would have been fielding a new generation of 27cm centimeter radars and also been more able to exploit H2S technology. I believe they had a 20cm 5kW radar named eisbaer (ice bear of polar bear) as early as 1941.

My understanding is that the 1.5m dish 27cm wavelength Euklid radar for FLAK direction was a development of the 27cm wavelength “Mannheim K” radar which itself was a development of the 54cm Mannheim radar a radar which also achieved track locking in late 43 or early 1944. Mannheim K was later meant to develop into the 9cm Mannheim KK which was in fact developed into “Rotterheim” using a magnetron a few of which saw service as FLAK laying radars in the defence of Hamburg.

Trenkle also notes that in 1942 Lorentz was 80% ready in development of a 25cm gun laying radar and left the field for lack of orders!

Instead the focus went to radars using existing frequencies which were to become more powerful and sophisticated. For instance Wurzburg-Riesse Gigant achieved 160kW pulse power however even the 8KW pulse ower Wurzburg Reisse when equiped with the k-laus circuit and windlaus could use coherent pulse Doppler to filter out not only static clutter such as windows and ground clutter without degradation of range and frwuency agillity but also windows carried by high altitude winds when used on Wurzburg Reisse k-laus could function with heavy jamming.