I would agree in essence with Britian being an island and all, but in the sphere of a Global War which was the reality in this era, U-boats threatend the vital existance of everyone. Here is an example of how Russia relied on the Atlantic Crossing for survival..

The list 1 below is the amount of war matériel shipped to the Soviet Union through the Lend-Lease program from its beginning until 30 September 1945.

Aircraft 14,795
Tanks 7,056
Jeeps 51,503
Trucks 375,883
Motorcycles 35,170
Tractors 8,071
Guns 8,218
Machine guns 131,633
Explosives 345,735 tons
Building equipment valued $10,910,000
Railroad freight cars 11,155
Locomotives 1,981
Cargo ships 90
Submarine hunters 105
Torpedo boats 197
Ship engines 7,784
Food supplies 4,478,000 tons
Machines and equipment $1,078,965,000
Non-ferrous metals 802,000 tons
Petroleum products 2,670,000 tons
Chemicals 842,000 tons
Cotton 106,893,000 tons
Leather 49,860 tons
Tires 3,786,000
Army boots 15,417,001 pairs