The losses of merchant ships caused by U-boats throughout 1940 are telling. In January and February, we deplore the loss of 85 boats, for a total of 290,000 tons. In March, April and May, a large number of U-boats having been withdrawn from the Atlantic to take part in the Norwegian campaign, the losses were limited to 43 boats — 140,000 tons. But in June, the submarines reappeared and, moreover, extended their field of action in the Atlantic.
Losses then amounted to 58 ships — 284,000 tons. For the rest of the year, the numbers are in line. British shipyards could not make up for these losses.
Many buildings built before the war still flew under the British flag, but the figure of the losses was not any less alarming, in spite of the contribution of Norwegian and Dutch elements that the invasion by Germany of the countries of the Western Europe had caused in April and May. And, at that time, the German submarines were far from having reached their maximum number.