[Homer_J_Simpson]

If you step back and look at the strategic importance Britain placed on the Bismarck threat, it seems they really were fearful of the damage the ship could do to convoys.

With good reason. That finally sank in for me a while back when I re-read the chapter in Wouk's The Winds of war that covers this period. The main characters are discussing the matter on May 26. Captain Henry says, ". . . unless the Bismarck is undamaged. In which case heaven keep any convoys she runs across. With that fire control she displayed, she'll pick off forty ships in half an hour."

For the first time I thought about the impications of that line. It means Bismarck could wipe out an entire convoy just like that. Britain couldn't afford to lose a whole convoy. Once would be a catastrophe. A second might have had them sending feelers to Berlin. That is what is at stake in the battle now beginning.

[abb]

Bismarck - Radar
FuMO 23 Radar

http://www.battleshipbismarck.com/bismarckclass/layout/13_bismarck_radar.php

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http://www.kbismarck.com/controltiri.html

Detail of the foretop command post with its rotating dome over it. 1/100 Model of Markus van Beek.

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.

Bismarck Rangefinder. This is the aft rotating dome over its command post. This station was under the command of the Fourth Artillery Officer, Kapitänleutnant Burkard von Müllenheim-Rechberg who was one of the few survivors from the ship.

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.1 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. The anti-aircraft fire was directed by four command posts, each equipped with a 4-meter rangefinder. Two of these command posts, covered by spherical cupolas (Wackeltopf), were on either side of the foremast, and the other two uncovered posts amidships aft.

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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http://www.hmshood.com/history/denmarkstrait/bismarck1.htm

The Veil is Lifted
Back at Scapa Flow on 22 May, Tovey was now faced with a decision about whether to sail himself. If the German fleet had left Bergen, they may already be nearing a breakout into the Atlantic. If he delayed sailing, then he may not be in time to assist in the battle to prevent the German breakout. On the other hand, if he sailed now and Bismarck was still waiting at Bergen for an improvement in the weather, he may find himself returning to port for lack of fuel at a critical moment.

To Tovey’s assistance came the small Naval Air Training Station at Hatston, Scapa Flow. The commanding officer, Captain Henry St. John Fancourt, thought it possible for a single aircraft to fly to Bergen to ascertain whether or not the German ships had sailed. Lieutenant Noel Goddard volunteered to pilot one of the base’s Marylands that were used for target towing. Accompanying Goddard would be the highly experienced navigator and observer Geoffrey Rotherham. Tovey’s permission for the venture was obtained, and at 1630 hours the aircraft took off. After a daring flight close to the sea, Goddard and Rotherham arrived at Bergen to find that the German vessels were no longer there. An urgent message was sent back to Hatston that Rotherham was able to confirm in person when he returned just before 2000 hours that evening.

So Admiral Tovey was at last certain that the German ships were no longer at Bergen, but the uncertainty about enemy intentions still remained. Various explanations could be offered about what might be taking place:

The German ships may be leading a convoy containing important stores or troops to northern Norway.
They may be part of a raiding force bound for Iceland.
They may be attempting to break out into the Atlantic.

He felt that the last possibility was still the most likely. It was also the one that posed the greatest potential risk. Tovey knew that the German ships would wreak havoc on the convoys if they were to succeed in breaking out into the Atlantic. Also, once out they would be almost impossible to track down. They had to be stopped before they got into the Atlantic.

New plans were urgently formulated to give the Home Fleet the greatest possibility of intercepting the German ships before they broke out. It had been 29 hours since Bismarck had last been sighted at Bergen – depending on when they had sailed, they may, even at that moment, be close to achieving their Atlantic objective. The following directions were issued to update Tovey’s previous disposition orders:

Suffolk at Hvalfjord, was ordered to sail immediately to join with RADM Wake-Walker in Norfolk, on patrol in the Denmark Strait.

The cruiser Arethusa, also at Hvalfjord, was to join Manchester and Birmingham. The three cruisers were to patrol the Iceland/Faeroes passage.

VADM Holland’s squadron of Hood, Prince of Wales and the destroyer screens were on their way to Hvalfjord to refuel before commencing their patrol. They were now ordered to proceed immediately to their patrol. They were to operate north of 62 degrees latitude and would be ready to react and cover the German ships should the cruisers patrolling either the Denmark Strait or the Iceland/Faeroes passage locate them.

Tovey himself sailed from Scapa Flow in his flagship King George V at 2245 hours on 22 May. They were accompanied by the aircraft carrier Victorious, the cruisers Galatea, Aurora, Kenya, and Hermione. The squadron also included seven destroyers (Inglefield, Intrepid, Active, Punjabi, Windsor and Lance). The group would be further reinforced off the Butt of Lewis when the battle cruiser Repulse and three more destroyers joined from the Clyde.

This latter squadron would act as a further backstop, operating behind Hood and Prince of Wales, south of the line of 62 degrees North latitude. Tovey gave consideration to detaching two of the cruisers of his squadron to patrol the Faeroes/Shetlands passage but decided against this. The chance of this passage being used by the German ships was small due to the proximity of the Home Fleet base at Scapa Flow in the Orkneys.

The naval units would be supported in their search by air reconnaissance patrols between Greenland and the Orkneys as well as sweeps along the Norwegian Coast.