Vice Admiral William S. Sims, Commander, United States Naval Forces Operating in European Waters, to All Naval Forces Operating in European Waters
23 March, 1918.
From: Force Commander
To : All sea forces.
Subject: Tendencies of German Submarine in attack.
The following figures from British Admiralty Reports are quoted for information:
Although a total of only 110 Merchant Vessels, British Allied and Neutral, were sunk in February – the lowest figure of any month since July 1916 – the percentage of success in attack has increased from 53.4% for January to 58.3% for February. This increase was mianly <mainly> in the English Channel and on the West Coast,where the January percentages of successful attacks were 49% and 44.4% respectively.
There was a decided increase in the proportion of attacks on vessel in convoy, the number in February representing 12% of the total attacks, compared with 5% in January.
Of the total losses, 62.5% were in Home Waters, the increased percentage over January being due to heavier losses – 16 compared with 8 – in the Irish Sea. The Mediterranean losses represent 22.8% of the total, compared with 34.5% for January.
But for the last 5 months, the percentage of losses to sailings for this Irish Sea is8% compared to 1.4% of the total sailing to and from all United Kingdom ports.
Attacks during constant light and darkness have decreased; but as the days lengthen, a decided increase is shown in the number of attacks between the hours of 4.p.m. and 9 p.m.
The number of attacks in Home Waters when the moon was up fell in February to 25% of the total attacks, the figures for January being 56%, but the percentage of success shows an increase, it being still well above that for daylight attacks. The losses of British vessels in United Kingdom overseas trades was 38%, double the January figures, but the same as those for December.
There was a slight tendency to attack f<a>rther from shore than in January.
N. C. Twining
Source Note: Cy, DNA, RG 45, Entry 517B. Document reference: “11-0-16/E/J/H/S.”