It aimed at interdicting German seaborne commerce with the Soviet Union, Sweden, Finland, Estonia and Latvia. In particular, an objective was to stop the flow of Swedish iron ore to Germany .
The driving force behind the project was the newly appointed First Lord of the Admiralty Winston Churchill and the head of planning was Admiral of the Fleet Lord Cork. Events overtook the project and it was never carried out.
Churchill proposed a substantial naval squadron: three Revenge -class battleships , an aircraft carrier, five cruisers, two destroyer flotillas , submarines and supporting auxiliaries. The battleships would need to be significantly modified to resist air and submarine attack as well as pass through the shallow waters.
Royal Sovereign would have been fitted with very large bulges to her hull (making her 140 ft wide) to increase her buoyancy and so reduce her draught by 9 ft (2.7 m) even after the addition of 4 to 5 in (100 to 130 mm) of deck armour (some 2,000 tons of armour would be used in total). While only two of her main turrets would be retained, elevation for those guns would be 30 degrees. In this new state her top speed would have been about 13-14 knots in action.
As well as cutting off German iron ore supplies, Churchill anticipated that this show of force would encourage the Scandinavian nations to join the war against Germany.
The First Sea Lord Admiral Sir Dudley Pound opposed the plan.
The arguments against were several. The armour plating was in short supply and was needed elsewhere; the three battleships were badly needed, particularly if Italy and Japan also declared war; the impact of air power was underestimated in the plan; the loss of such a squadron would encourage Italy and Japan to declare war.
Despite these cogent arguments, and widespread opposition, Churchill continued to push hard for Catherine. Pound avoided a "head-on" argument and apparently cooperated, but pointing out problems as he did so. Eventually, on 20 January 1940, after six months, Churchill himself shelved the operation.
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