A British writer, A. H. Pollen in his book The British Navy in Battle, wrote that
"between June, 1917, and January, 1918, was seen the slowly growing mastery of the submarine. The rate of loss was halved. In April, defeat seemed to be only a matter of a few months away. By October it had become clear that the submarine could not by itself assure a Germany victory."
Admiral Sims called the convoy system the "most important agency in frustrating the submarine." Toward the end of the war
"from 91 to 92 per cent of Allied shipping sailed in convoys. The losses in these convoys was less than 1 per cent."
Shipping losses, which had reached their high point in April, 1917, with 875,023 tons sunk, dropped steadily to a low of 112,427 in the last full month of the War, October, 1918.
However, even as late as the end of the summer of 1918 many Germans, and most U-boat men, had no idea how decisively the war had turned against them. In France the last great German drive for Paris and victory had been stopped at the Marne River. From August onward the German Army was in steady retreat.
The rate of loss of U-boats was climbing, while the rate of their success against merchant ships was declining. In one particularly disastrous sortie from the Flanders submarine base in 1918, eighteen U-boats set out on patrol and only two returned.
With defeat in sight, the U-boat flotilla at Cattaro on the Adriatic Sea was ordered back to Germany. Though Allied warships lay waiting to intercept them at Gibraltar, all slipped through except the U-34 under Lt. Comdr. Johannes Klasing, destroyed on the night of November 8-9 by the British Q-boat Privet.
Nearby on the same night the UB-50 under Lieutenant Commander Kukat found the British battleship Britannia in range and fired two torpedoes into it. When the Britannia sank two hours later, it joined the company of four other British battleships sunk during the war by U-boats' torpedoes — the Triumph and Majestic, sunk by Hersing in the U-21 at Gallipoli; the Cornwallis, sunk in the Mediterranean Sea; and the Formidable, sunk in the English Channel with heavy loss of life on the stormy New Year's night of 1915.
Two days after the sinking of the U-34 and the Britannia — the last U-boat and the last warship to be sunk — the war was over. In the course of it, German submarines had sunk slightly more than 18 million tons of shipping, including 349 British warships and a total of between five and six thousand merchant ships.
By the end of the war in 1918, Germany, which started with only twenty-eight submarines in 1914, had completed or nearly completed some six hundred. Keels for 811 U-boats had been laid. Of the 199 U-boats lost, 178 were sunk in action. Seven others were interned in neutral ports, and fourteen damaged ones were destroyed by the Germans themselves. (Twenty of the 178 sunk in action were victims of the torpedoes of Allied submarines.)
The relatively few thousand Germans assigned to duty in U-boats tied up a quarter of a million men on the Allied side, engaging them either in fighting the U-boats directly or in replacing the ships the U-boats sank.
Surprisingly, the British lost almost as many submarines in the course of the war as the Germans did — 175. The British submarine force achieved nothing like the spectacular results of the U-boats (principally because German shipping had virtually disappeared from the high seas long before the end of the war), but they did have considerable success. By attacking the Baltic shipping lanes between Germany and Sweden they disrupted traffic in iron ore to Germany. Operations in Turkish waters were particularly successful as well.
After the Armistice, 138 U-boats surrendered to the Allies. One U-boat which did not reach a British port with the others was Hersing's U-21, which, by sinking the Triumph and Majestic at Gallipoli, was perhaps responsible for turning the tide there in 1915. For some reason never known, the U-21 sprang a leak while in tow of a British ship and promptly sank. (The British suspected skullduggery, and were probably right.)
Von Arnauld's last U-boat command, the big new submarine cruiser U-139, was taken by France. On its maiden voyage with a French crew it sank with all hands. The cause of its sinking, like that of the U-21, was never learned.
And so the first war in which submarines had played a part — and that part a nearly decisive one — was over.
It was not to be the last.