In the original Timeline
Bismarck was scheduled to return to Kiel on 24 January 1941, but a merchant vessel had been sunk in the Kiel Canal and prevented use of the waterway. Severe weather hampered efforts to remove the wreck, and Bismarck was not able to reach Kiel until March.[18] The delay greatly frustrated Lindemann, who remarked that "[Bismarck] had been tied down at Hamburg for five weeks ... the precious time at sea lost as a result cannot be made up, and a significant delay in the final war deployment of the ship thus is unavoidable."[22] While waiting to reach Kiel, Bismarck hosted Captain Anders Forshell, the Swedish naval attaché to Berlin. He returned to Sweden with a detailed description of the ship, which was subsequently leaked to Britain by pro-British elements in the Swedish Navy. The information provided the Royal Navy with its first full description of the vessel, although it lacked important facts, including top speed, radius of action, and displacement.
If Captain Lindemann's statement was correct that might advance the departure of Prinz Eugen and Bismarck from Gotenhafen from 18th/19th May to 11th/12th April.
I've had a look on the Naval-History.Net website to see what King George V, Prince of Wales, Hood. Repulse, Renown, Ark Royal, Victorious and Furious were doing around the 11th/12 April 1941 IOTL.
Most of them were either...
- Off Brest in case The Twins tried to break out.
- In transit from Scapa Flow or Gibraltar to Brest to relieve the ships currently on station or
- In transit from Brest to Gibraltar or Scapa Flow having been relieved of blockade duty.
The exceptions were:
- Prince of Wales
- 1st to 26th April- The PRINCE OF WALES was at Scapa Flow carrying out working up exercises. Gunnery exercises were severely curtailed due to the continuing problems with the quadruple 14in turrets. The work up included checking radar performance and the calibration of air warning and fire control equipment.
- 27th April - It was on this day that the last of her three turrets was accepted from Vickers Armstrong and practice drills with all her armament could commence.
- (The PRINCE OF WALES went to sea with HACS IVGB, with full radar ranging systems, and no less than nine AA fire control radars: four Type 285 Radars, one on each High Angle Director Tower and four Type 282 Radars, one on each Mk IV pom-pom director, and a long range Type 281 Radar which also had precision ranging panels for aerial and surface targets. This placed the PRINCE OF WALES in the forefront of naval HA AA fire control systems at the time)
- 8th May - Carried out Full Power Trials.
- 21st May - Ship reported to CinC Home Fleet as ready for Fleet service.
- (The PRINCE OF WALES had had less than two months working up, which was completely inadequate considering all the new systems and the fact that 80% of her crew were Hostilities Only and had never been on a ship before. Further she still had major problems with her main armament and 100 Vickers Armstrong staff were embarked attempting to fix the problems. The BISMARCK in contrast had worked up over a period of five months and was fully operational and efficient)
- Victorious
- March 29th - Commissioned for service in Home Fleet after work-up.
- April - Contractors sea trials and passage to Rosyth.
- Prepared for operational service.
- April 15th - Joined Home Fleet.
- May - Final Acceptance Trials and worked-up for service.
- May 20th - Embarked of aircraft and intended to Join Convoy WS8X escort.
- Furious
- April - Deployed to carry aircraft to Gibraltar for transfer to HM Aircraft Carrier ARK ROYAL.
Apart from Prince of Wales (which was more
"worked down" than OTL) the only British fast capital ship at Scapa Flow was King George V which was present from 10th to 13th April. Although Hood would arrive on 15th April.
However, there's no guarantee that the ships would be in those places ITTL because the Admiralty might have suspected that something was afoot. E.g. air reconnaissance might have revealed Bismarck's earlier than OTL move to the Baltic so they'd expect that the ship would complete her working early in April 1941 instead of late May 1941 and from the beginning of April 1941 take as many precautions as possible.
Also the Naval History Net entry on King George V says...
From about the 14/5/41 the CinC Home Fleet and the Admiralty became aware that the Luftwaffe had increased its reconnaissance of Scapa Flow. Also Luftwaffe Enigma decrypts revealed that FW 200's were carrying out reconnaissance flights between Jan Mayen island and Greenland checking out the ice conditions. This intelligence led to the possibility that German ships were intending to break out into the Atlantic.
My guess is that the Naval History Net of TTL would say...
From about the 7/4/41 the CinC Home Fleet and the Admiralty became aware that the Luftwaffe had increased its reconnaissance of Scapa Flow. Also Luftwaffe Enigma decrypts revealed that FW 200's were carrying out reconnaissance flights between Jan Mayen island and Greenland checking out the ice conditions. This intelligence led to the possibility that German ships were intending to break out into the Atlantic.
IIRC from reading Ludovick Kennedy's Pursuit the British had a spy in the dockyard at Brest who knew about the impending sortie of Bismarck and Prinz Eugen IOTL and he was able to inform the Admiralty. IIRC from the book that was how the Admiralty first learned about Operation Rheinübung.
That spy might be able to do the same ITTL.