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A Stabilisierte Leitstand ( English: stabilized director post), abbreviated SL, is a fire control element in German World War II era shipborne heavy anti-aircraft defense. One to four SL's were installed on all capital ships of the Kriegsmarine. A Stabilisierte Leitstand measured distance, bearing and height of the target. Angles for bearing and height were taken through an optical sight, whilst distance was measured with a stereoscopic rangefinder. The director post was stabilized on three axes: against pitch and roll so that measurements were taken in a horizontal plane. Stabilization against yaw kept the director post trained on the target even when the ship was turning. The measured data was processed by a director analog computer (German: Rechengerät) to calculate settings for the anti-aircraft battery.

Operation

The anti-aircraft artillery officer assigned targets to the Stabilisierte Leitstand. On German capital ships the anti-aircraft artillery officer was usually the second artillery officer ( "II AO" ), the first artillery officer ( "I AO" ) being responsible for the main artillery. The II AO selected targets from the anti-aircraft operation post (German: Fla-Einsatzstand), usually situated on the foretop of the ship. The anti-aircraft operation post was equipped with target selection devices (German: Zielanweisegerät, "ZAG" ), that transmitted the target's bearings to the Stabilisierte Leitstand. The ZAG was also stabilized on three axes. If there were multiple director posts and multiple anti-aircraft batteries then the II AO had also a switchboard to configure which battery/batteries a director post was guiding.^[1]^[2]^[3]^[4]

A twin 10.5 cm anti-aircraft gun, showing the fuse setting mechanism on the outer side of the protective shield

The Stabilisierte Leitstand was manned by four people:^[5] two aimers for the bearing and height angle sat backwards to the target whilst the control officer and the rangefinder were facing the target. Once a lock on the target was acquired the control officer signalled permission to fire to the director computer.^[6] From then on measurements could be fed to the director computer either intermittently or in continuous modus. As aircraft targets shifted range quickly, usually the measurements were fed in continuous modus.^[7]

The measured angles and distance measured by the SL were transmitted to a director computer which calculated the angles for the connected anti-aircraft batteries. Each SL director had its own anti-aircraft director computer. This computer also calculated the fuze settings and triggered the firing clock. The fuze setting mechanism was mounted on the outside of the protective shield for the anti-aircraft battery. The computer gave a horn signal when the round was set and had to be loaded into the gun and gave a bell signal when the gun had to be fired. The gun loaders could load a round on the fuse setting mechanism from inside the protective gun shield, which was open anyway towards the rear of the gun mounting. As the guns could not be mounted in turrets, there was no central ammunition feed.^[8]^[9]^[10] Munition had to be fetched from nearby munition hoists over the open deck which was a risky operation during attack.^[11] When the main battery was firing trained at extreme rotation angle, the blast of these guns rendered the operation of any nearby open anti-aircraft battery impossible.^[12]

As the heavy anti-aircraft battery was also the Secondary armament on cruisers, a SL director was also able to lock on sea targets. Depending on the nature of the target a different fire control was used: for fast moving small targets the director kept firing in anti-aircraft modus with time fuzes but for larger distances only independend fire was possible, or directed fire with limited assistance of auxiliary elements of the central director computer, used by the main battery.^[6]^[1]

three gun aimers. ^[11]^[13]

Fire Control

kant/kipp ^[14]
seeziel <> luftziel : target <> firing
inner/outer SL : feedback from director computer and directly feeding of kant angle

Versions

In 1925, an experimental anti-aircraft fire control system was installed on the light cruiser Köln, consisting of a stabilized director, a rechengerät and four 8.8 cm SK C/25 naval guns in twin mountings. The director was stabilized by two levers, which kept the director in a horizontal plane. The guns were mounted on tilting trunnions, making the gun mountings three axial. During tests, the stabilization proved to be unsatisfactory. The guns mounting proved to be unsatisfactory as well: there was too much distance between the two guns, when fired this caused the mounting to swing. In order to mount the guns as close as possible to the center of the gun mounting, the kant axis was introduced properly.^[15]^[16]
The first cilindrical leitstand SL-1 was installed in 1933 on the light cruiser Leipzig. The SL-1 was equipped with an optical rangefinder with a base of 3m.^[17] The horizontal stabilisation of the director was now regulated with sliding weights mounted on two axes. The director received also stabilization against yaw. The kant and kip angle were also stabilized. For stabilization a 53 cm gyroscope and twenty engines were needed. During tests the director was easily offset by non-uniform distributed forces, like wind or crew movements. As the axes of the gyroscope tended to drift easily by the movements of the ship, an extra device (German: Horizontprüfer) was needed to measure the horizon and to recalibrate the gyroscope. Test were executed with the three-axial twin 3.7 cm SK C/30 gun mounting, as the three-axial gun mounting for the heavy anti-aircraft gun was not yet ready.^[18] Eventually all five light cruisers were equipped with one SL-1 on the afterdeck and six or eight 8.8 cm SK C/32 naval guns in twin C/32 mountings.^[19]
The first heavy cruiser of the Kriegsmarine Deutschland was equipped with two improved SL-2's in 1934 for directing its six 8.8 cm SK C/31 naval gun mounted in twin C/31 mountings These directors were installed on either side of the battle mast.^[19] In the SL-2 the drifting of the gyroscopes was neutralized by pendula, and hence the very expensive Horizontprüfer could be omitted.^[20]^[21]
Two SL-4's were installed on the next two Deutschland-class heavy cruisers Admiral Scheer and Admiral Graf Spee.^[11] Tests executed in 1936 showed that the yaw stabilization was insufficient to cope with sharp changes of course. These directors still did not allow for any Parallax correction. A parallax correction takes into account the difference in position on the ship of the director and the gun. Since both guns and directors were placed close enough on all the ships, the size of the multiple shell explosions was thought to compensate for the relative small parallax error.^[20]
The two Scharnhorst-class battleships Scharnhorst and Gneisenau and the first two Admiral Hipper-class heavy cruisers Admiral Hipper and Blücher received each four SL-6's.^[22] Apart from improved yaw stabilization, these directors were the first to have Parallax correction and a spherical shield which protected the operators against weather and shell splinters.^[23] The optical rangefinder on the SL-6 had a 4m base.^[4]^[5] The Scharnhorst-class battleships were equipped with fourteen 10.5 cm C/33 guns, mounted in seven twin C/31 mountings. Three mountings each were placed very close together on port and starboard, but the seventh was placed at the aft superstructure, just behind the aft main battery turret. The port and starboard batteries had a satisfactory parallax correction, but not the seventh battery. This battery needed an additional parallax corrector which proved unsatisfactory. The Admiral Hipper-class heavy cruisers were equipped with twelve 10.5 cm guns. Since the aft pair of mountings was placed close together, one common parallax point placed between these gun mountings was configured for these guns.^[24] The SL-6 weighted 46 ton and was very delicate equipment as it was easily put out of order by light shocks.^[25]

The concical shape of the SL-8 are easily recognized on the heavy cruiser Prinz Eugen
Both Bismarck-class battleships Bismarck andTirpitz and the third Admiral Hipper-class heavy cruiser Prinz Eugen were equipped with four SL-8's.^[22] The SL-8 was basicly a SL-6 model where the big, heavy gyroscopes were replaced by small gyroscopes which steered engines driving the sliding weights on the stabilization axes. These small gyroscopes were more precise and could be activated in less then two minutes. The use of small gyroscopes also saved a log of weight but this was partially nullified by the need to install a 5 ton balast.^[26] Total weight was reduced to 40 ton.^[27] The Bismarck-class ships were equipped with sixteen 10.5 cm guns, mounted in eight twin mountings. These were grouped in a forward and aft pair on port and starboard. in the middle of each pair there was a parallax point for the gun directors. Only two of the four directors on Bismarck received their full SL-8 equipment, the other two had temporary equipment installed but received no update before the Bismarck was sunk on its first mission. The fact that each gun mounting did not have its own director, the configuration of a parallax point between two near gun mountings, the parallax problem with the Scharnhorst-class aft gun mounting and the fact that Bismarck's forward two pairs of C/31 gun mountings were of a different type than the aft C/37 pair all lead to erroneous explanations about the poor performance of Bismarck's anti-aircraft defense against the attacks by the slow Fairey Swordfish torpedo aircraft.^[28] Bercuson&Herwig state that when the C/31 guns fired at the target, the C/37 guns aimed behind the target.^[29] Stephen claims the gun directors could not cope with air speeds below 100 mph.^[30] Schmalenbach mentions during his explanation of German fire control the presence of many false theories.^[28] Gimbal

Other developments

In 1932 the Kriegsmarine was also developping a combination of gun and director in one turret. Such a configuration had many advantages such as shorter signals lines between gun and diretor, central ammunition feed, protection and taking up less space on deck. However, when fired the smoke blast and vibrations interfered too much with the director equipment and this project was abandonned. When radar promised to solve the smoke problem, the project was picked up again, and it was intended to equip the heavy anti-aircraft defense of the H-class battleships with these turrets. Such a turret needed small gyroscopes which steered the stabilization with motors, not the big gyrostabilizators used in the SL. Once these small gyros became available, they were used in the SL directors.^[25]^[28]

The M42 was to become the last version of the SL series. It was a complete redesign with gyro steered engine stabilization.^[28]
Sverdlov

Citations

^ ^a ^b Schmalenbach 2001, p. 69. Cite error: The named reference "FOOTNOTESchmalenbach200169" was defined multiple times with different content (see the help page).
^ Draminski 2018, p. 24.
^ Schmalenbach 1993, p. 121.
^ ^a ^b Breyer 1991, p. 17.
^ ^a ^b Brennecke 2003, p. 284.
^ ^a ^b Schmalenbach 1993, p. 123.
^ Schmalenbach 1993, p. 126.
^ Schmalenbach 1993, p. 156.
^ Schmalenbach 2001, pp. 68–69.
^ Breyer 1991, p. 16.
^ ^a ^b ^c Stehr & Breyer 1999, pp. 26–27. Cite error: The named reference "FOOTNOTEStehrBreyer199926–27" was defined multiple times with different content (see the help page).
^ Brennecke 2003, p. 296.
^ Schmalenbach 2001, p. 68.
^ Schmalenbach 1993, pp. 16–17.
^ Schmalenbach 1993, pp. 116, 148.
^ Stehr & Breyer 1999, p. 18.
^ Breyer 1994, p. 10.
^ Schmalenbach 1993, pp. 116–117.
^ ^a ^b Stehr & Breyer 1999, p. 19.
^ ^a ^b Schmalenbach 1993, p. 117.
^ Prager 2002, p. 91.
^ ^a ^b Stehr & Breyer 1999, p. 27.
^ Schmalenbach 1993, pp. 117–118.
^ Schmalenbach 1993, pp. 118–119.
^ ^a ^b Koop & Schmolke 2001, p. 201.
^ Schmalenbach 1993, pp. 117–119.
^ Bercuson & Herwig 2003, p. 33.
^ ^a ^b ^c ^d Schmalenbach 1993, p. 118.
^ Stephen 1988, p. 92.
^ Bercuson & Herwig 2003, pp. 33–34.

References

Bercuson, David J.; Herwig, Holger H. (2003) [2001]. The Destruction of the Bismarck. New York: The Overlook Press. ISBN 978-1-58567-397-1.
Brennecke, Jochen (2003). Eismeer Atlantik Ostsee. Die Einsätze des Schweren Kreuzers Admiral Hipper [Arctic, Atlantic, Baltic: The Operations of the Heavy Cruiser Admiral Hipper] (in German). Munchen: Heyne. ISBN 3-453-87084-0.
Breyer, Siegfried (1991). Die Schweren kreuzer der ADMIRAL HIPPER-Klasse [The heavy cruisers of the ADMIRAL HIPPER-Class] (in German). Friedberg: Podzun-Pallas-Verlag. ISBN 3-7909-0429-5.
Breyer, Siegfried (1994). Kreuzer "Nürnberg" und "Leipzig" [Cruisers "Nürnberg" and "Leipzig"] (in German). Podzun-Pallas-Verlag. ISBN 3-7909-0507-0.
Draminski, Stefan (2018). The battleship Bismarck. Osprey Publishing. ISBN 978-1472828880.
Prager, Hans Georg (2002). Panzerschiff Deutschland, Schwerer Kreuzer Lützow: ein Schiffs-Schicksal vor den Hintergründen seiner Zeit [Armored Ship Deutschland, Heavy Cruiser Lützow: A Ship's Fate in the Circumstances of its Time] (in German). Hamburg: Koehler. ISBN 978-3-7822-0798-0.
Koop, Gerhard & Schmolke, Klaus-Peter (2001). The Heavy Cruisers of the Admiral Hipper Class. London: Greenhill. ISBN 1-85367-434-6.
Schmalenbach, Paul (1993). Die Geschichte der deutschen Schiffsartillerie [The history of German naval artillery] (in German) (3rd ed.). Herford: Koehler. ISBN 3-7822-0577-4.
Schmalenbach, Paul (2001). Kreuzer Prinz Eugen unter Drei Flaggen (in German). Hamburg: Koehler. ISBN 3782208234.
Stephen, Martin (1988). Grove, Eric (ed.). Sea Battles in close-up: World War 2. London: Ian Allan ltd. ISBN 0-7110-1596-1.
Stehr, Werner F.G.; Breyer, Siegfried (1999). Leichte und mitlere Artillerie auf deutschen Kriegsschiffen. Marine-Arsenal (in German). Vol. Sonderheft band 18. Wölfersheim-Berstadt: Podzun Pallas. ISBN 3-7909-0664-6.