# Independent fire control on WWII era battleships



## Demetrious (Oct 14, 2009)

I've been tremendously curious as to something involving fire control of battleships: if the primary rangefinders were destroyed, could each turret continue directing fire with backup rangefinders mounted on the turrets themselves?

I've done some reading on it (as much as the internet will allow,) and I understand that the primary radar or optical rangefinders on the central tower would take measurements and pass the data down to computers in the fire control room (protected deep inside the ship,) that would then pass the information to gun-laying servos. The gunlaying was completely automated on most ships by the mid-point of the war. But I have been unable to find any information as to what options the crews of each turret had should the upper superstructure of their vessel be thoroughly smote, and the rangefinders destroyed- or the connections between central fire control and the turrets destroyed by battle damage. 

Did these turrets have any local fire control ability, or would they be limited to firing completely blind on a pre-set pattern?


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## beaupower32 (Oct 14, 2009)

Most Turrets on a battleship had secondary way of using fire control via a localized sighting system. I will use the Bismark as a example. 

The fire of the main and secondary batteries was directed from the command posts, which were located forward, astern, and above the foretop platform. Each of these three posts mounted a rotating dome with an optical rangefinder and a FuMO 23 radar instrument. The command posts were connected by armoured communication shafts to the computation rooms under the armour deck forward (section XV) and aft (section VII). The FuMO 23 antennae had a rectangular shape and measured approximately 2 m. high and 4 m. wide. They had a frequency of 368 MHz, and operated on an 81.5 cm wavelength with a power-output of 9 kW at 500 kHz. The maximum effective range of this device was about 25,000 m. However, the German FuMOs were not equipped with the PPI (Plan Position Indicator) display system that is so familiar in today’s radars, but a simple A-scope display instead. Therefore, they could hardly detect more than one target at the same time, and bearings were not very accurate either. The lack of PPI was one of the reasons German capital ships were so redundant and equipped with three sensors.

The foretop command post, under the command of the First Artillery Officer (I.A.O.), was above the foremast, at about 31 meters above sea level. It was equipped with a 10.5 meter base range finder (Basisgerät BG), and had a visual field of 360º. The forward command post was attached to the forward conning tower, and had a 7-meter base rangefinder, however, due to the superstructure, its visual field was smaller. The after command post had a 10.5-meter base rangefinder of similar characteristics as the one in the foretop.

Each of the four main battery turrets ("Anton", "Bruno", "Cäsar" and "Dora") was equipped with a 10.5-meter base rangefinder too, and in case all three command posts were put out of action in battle, the turrets could then proceed individually to local fire.(The 10.5 meter base range finder in turret "Anton" was removed during the winter 1940/41, due to damage from sea water at high speeds.) However, the chances of scoring a hit with each battery firing on its own were less than under a centralized command. The central turrets of the secondary battery had also their own 6.5-meter base rangefinder. 

Shooting methods were different on each navy and depended on the number and type of guns, the distance to the target, and the type of rangefinder utilized. In order to find the range as fast as possible, on the Bismarck it was customary to open fire with three partial salvoes in rapid succession, set at different ranges, so that all three were in the air at the same time. Let's say turret "Anton" first, two seconds later turret "Bruno", and then turret "Dora". After observing the fall of this first group, the Artillery Officer had to introduce the necessary corrections and usually with the second group the target was already straddled. Once the correct range and inclination was obtained, then they could fire full salvoes with all eight guns, or partial salvoes with either the fore or after turrets.


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## Demetrious (Oct 14, 2009)

*Absolutely fantastic.* You are a scholar and a gentleman, sir. This is _exactly_ what I wanted to know, thank you.


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## Henk (Oct 15, 2009)

Thanks beaupower32 for the info.


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## beaupower32 (Oct 15, 2009)

Glad I could help. Any other questions, please let me know!


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## timshatz (Oct 15, 2009)

Should also mention there were both Optical and Radar based range finders on most capital ships by the end of the War. Results differed with regards to the Radar directed Fire Control as they could be confused by proximity to land or natural phenomina (wave heights, roster tails, ect). In at least one case, a BB with an older FC Radar used the splashes of another BB with a later mark FC Radar to target an enemy ship that it could not "see" with it's own FC radar. 

The actual FC director was typically well inside the ship. The guns were fired from this location. They could be fired locally (in the turret or mount) but mostly were fired from the FC room. As noted, in his excellent post, by Beau, the room was armored. The Computer itself was (going on memory here) about 4ft x 4Ft x 4Ft with a series of representations on the top of it (the top was rather like the top of a table with a glass top, the representations were underneath) showing your ship, the enemy ship, the speeds and relative bearings, shell type, distance, shell flight time, ect. It was a large, mechanical computer and was very, very cool to watch in operation. Cracked open, it was litterlly a maze of gearing and wiring. 

One other point. The trick of Surface Gun shooting was getting the range and deflection right. Range was how far away (pretty obvious but needed to be said) and was based on both optical and radar range finding (with radar taking the lead in most cases in the US Navy). The deflection was a function of guessing the speed of the opposing ship based on observations and calcuations based on change in angle given the distance. The trick was to get something called a straddle on the opposing ship. That was where your shells landed on either side of the ship, in line with the ship as viewed from your ship (neither behind or in front of it). Once that happened, you had the range. From there on, most shooting was done based on the Gunnery Officer's prefered method of shooting.

The trick was not to shoot directly at the target but to spread your shots out so they landed on a 200 yard spread (just picking a random number) with the target being in the center so at least some of the shots hit. You were trying to get as high a percentage as possible on target with each shot, no necessarily trying to make every shot hit. So, using Beau's example, the Bismark would fire a salvo that would ripple down the side of the ship, A turret through to D turret with a small delay (1 or 2 seconds) between turrets. Each turret would fire at a varied distance to bracket the target. If the target were at 15000 yards, A turret would fire at 14,600, B turret would fire at 14,800, C turret would fire at 15,000 and D would fire at 15,200. So the target would get a hit by at least one of the turrets. Then, the Gunnery Officer would "Rock the Ladder" where he would set the lower end of the range to 14800 (upper edge at 15,400) and fire the next salvo. Back and forth, the ladder is rocked, up and down, keeping the manuvering target in (or close to) the center of the rocking. It was one of the ways the gunnery was done in surface combat, and it was a good one (a lot of gunners used it).


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## Henk (Oct 19, 2009)

Oh, actually it is spelled Bismarck guys. lol


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## hartmann (Oct 24, 2009)

Hello to all ¡

I would like to add some corrections to the good post of Beaupower 32.



> However, the German FuMOs were not equipped with the PPI (Plan Position Indicator) display system that is so familiar in today’s radars, but a simple A-scope display instead.



That´s not correct. All the FuMOs with Lobe switching had a "J" or a "B" display, not the primitive "A".
BTW, a conventional display is far more precise than a PPI. 
Also, a lot of Allied ships, lacked PPI displays even late in the war because It was very expensive and difficult to upgrade or change the earlier radar sets. By example, the Type 271 was not equiped in the first series with PPI, but only with a common "A" display.

Discounting the fact that the PPI is not an Allied invention, but a German-British invention (both countries discovered this display in 1940 allmost simultaneously).

The main advantage of PPI displays is that You can understand the pips like a map (far more easy than in a conventional display), but It´s less accurate.

All the late war Allied fire control had *one master* "B" (or "J") display and various *slave* PPI displays (the Mark 8 mod3 or the late Mark 13 mod0 are fair examples of this).



> Therefore, they could hardly detect more than one target at the same time, and bearings were not very accurate either.



No, that´s not exact also. The prototipe "Seetakt", which carried lobe switching and the late war set FuMO 26 (1943) or the earlier FuMO27 (with lobe switching of 1941) were far more precise than allmost all the previous Allied radar sets of the 1940 and even mid 1942 years (like plain Type 284 or Mark 3). 

When We compare accuracy, the only radar sets similar to the FuMO 26 were the US Navy Mark 8 and the British Type 274/277. The bearing accuracy of those 3 radars was very similar between them, not exceeding the 50 metres of bearing accuracy and the 0,2-0,5º of angular azimuthal accuracy.



> The lack of PPI was one of the reasons German capital ships were so redundant and equipped with three sensors



Again, this is not exact. 
All the warships carried at least two gunlaying radar sets, because of redundancy security If one set was disabled. 
It had nothing to do with lack of acccuracy or similars. By example, the mid war set FuMO63 "Hohentwiel" had a master "B" display and 1 or 2 slave PPI displays, like the Allied ships. This is even more 
marked in the late FuMO 8x "Berlin" surface series (a "B" or "A" display and 2 or even 4 PPI slave displays).

I hope this will be helpful


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