German Submarine Warfare 1914-1918 in the Eyes - British Naval ...

Table 14: U-boat merchant war Sep. 1916 to Sep. 1917 56
North Sea+Atlantic Mediterranean
U-boats BRT sunk U-boats BRT sunk
out on torpe- per U- out on torpe- per U-
merch.
doedboat merch.
doedboat war per
w/o and day war per
w/o and day
day Total warning out day Total warning out
1916 Sep 5 110 194 2 % 672 3 90 315 30 % 951
Oct 15 205 142 10 % 433 6 105 473 68 % 583
Nov 13 149 403 7 % 379 8 89 944 59 % 358
Dec 13 166 093 9 % 414 8 108 400 83 % 437
1917 Jan 17 232 642 13 % 447 4 58 720 81 % 485
Feb 23 371 065 47 % 574 8 98 606 68 % 463
Mar 27 438 426 64 % 515 8 53 288 84 % 212
Apr 31 615 338 60 % 661 11 193 869 72 % 602
May 29 412 513 61 % 459 11 125 994 64 % 358
Jun 34 507 925 74 % 493 12 109 768 56 % 311
Jul 31 424 878 76 % 443 8 62 750 82 % 254
Aug 30 390 689 81 % 417 10 54 977 73 % 186
Sep 35 257 083 72 % 245 12 63 919 83 % 183
*Grey=Unrestricted Submarine Warfare
The percentage of tonnage sunk without warning grew immensely from
around 10% in the restricted to 60-80% in the unrestricted phase. In the four
months of restricted warfare, October, 1916 – January, 1917, the average sinking
rate in North Sea and Atlantic was around 418 BRT per boat and day. In the first
four months of the restricted phase the daily tonnage sunk increased by 25% to 552
BRT.
Likewise, in the Mediterranean there was no correlation between the amount
of tonnage sunk per day and the manner of sinking, i.e. with or without warning.
The numbers vary wildly depending on the submarine commander, his crews, the
boat, weather and fortune. 57 To illustrate, we need only compare September, 1916
with the same month a year later.
With the increase of deployed boats and targets from February 1917 on, there
is no jump in the tonnage sunk in the Atlantic.
56 Numbers based on: NA, HW 7/3; NA/ADM 137/3921; NA, ADM 137/4817; NA, ADM
137/4814; NA, ADM 1/8509/1; Spindler, Handelskrieg; Bendler, UB- und UC-Boote.
57 See also for this: Schröder, Uboote des Kaisers, pages 325-329.
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