When in February 1917 Germany started the unrestricted submarine campaign, the number of merchant ships sunken by U-boats increased, reaching its peak in April that year. From that time the number of vessels sunk started to decrease. However, a more detailed study of the number of ships sunk while navigating the area between the north Iberian peninsula and the Portuguese-held archipelagos of the Azores, Madeira and Cape Verde, shows a different reality. In this vast area, through which most of the Allied maritime traffic sailed, there was only a real decrease in ships sunk from May 1918. This article, using mainly primary English, German, French and Portuguese sources, shows this lesser-known reality and aims to give some possible explanations for this situation.

中文翻译：

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大西洋中部的护航系统，1917-1918

1917 年 2 月德国开始无限制潜艇战役时，被 U 型潜艇击沉的商船数量增加，并在当年 4 月达到顶峰。从那时起，沉没的船只数量开始减少。然而，对在北伊比利亚半岛与葡萄牙控制的亚速尔群岛、马德拉群岛和佛得角之间的地区航行时沉没的船只数量进行的更详细研究显示了不同的现实。在大部分盟军海上交通航行的广阔地区，自 1918 年 5 月起，沉没的船只仅真正减少。本文主要使用主要的英语、德语、法语和葡萄牙语来源，展示了这一鲜为人知的现实和旨在对这种情况给出一些可能的解释。