War+At+Sea-+Allied+Countermeasures+to+U-Boats

The main reason that the U-Boat Campaign had lost momentum during the end of 1917 was because the Allied side had successfully developed countermeasures to the U-Boat threat. Defensive measures had initially included arming merchant ships. Merchant ships were also advised to escape or to steer towards the U-Boat in an effort to ram it or force it to submerge. The armed merchant ships also engaged the submarines in gun battles, sinking 2 U-boats in 1915. Earlier variants on escorting were also developed, with small merchant vessels escorted by submarines. These measures had been all highly effective in protecting ships against U-Boat attacks. However, there are tactics that had were extremely expensive yet had yielded minimum results. These tactics were offensive strategy, meaning instead of protecting merchant ships, aimed to directly hunt for and bring down U-Boats. This included using nets to trap submerged U-Boats then use explosive sweeps to destroy them. This was a failure. The Dover Barrage was also set up, which was the campaign to close straits, such as the Dover strait with minefields and boom nets. Minefields were also laid around the German U-Boat bases as well as patrolling them with Allied Submarines. However, they all met little success; the above strategies had only yielded the sinking of two submarines in 1915.

Q Ships Another highly successful tactic used by the Allies were the so-called 'Q-Ships', also called 'Decoy Vessels'. They were a military secret at that time. Because during that period, depth charges were relatively primitive. Main methods to sink a submarine was to shoot it or ram it, though that requires the submarine to surface. Q Ships were essentially old, expendable steamers armed with hidden artillery and torpedoes. They which operated under the principal to lure submarines who are tricked in thinking these ships were merchant vessels to the surface. Because they are disguised as easy targets, submarine captains may choose to attack them with deck guns, where ammunition was in a more abundant supply, instead of torpedo. Stuffed with cork, Q-ships were very hard to sink even if they were hit by a torpedo. . After that, the ships would open up the artilleries and shelled the U-Boat as quickly as possible. The first solo victory by a Q-ship over a U-Boat came on 24 July, 1915. During the entire duration of the War at Sea, 14 U-Boats were sunk and 60 damaged at the cost of 27 Q-Ships out of 200 built, U-Boats being more expensive than Q-Ships. 10% of all submarines were sunk by Q-Ships. Convoys Convoys were systems involving merchant shippings travelling together in a pack escorted by naval vessels, concentrating the need for defense together reduces the chance U-Boats catch hold of lone ships. However, at the beginning, were extremely unpopular with naval captains, although there were earlier successes with convoy sailing. The reason was that the convoy system posed severe delays on shipping schedule, reducing the capacity the current maritime trade system and therefore creating a situation desired by the Germans. When the threat of U-Boats became too large to ignore, the British admiral adopted the convoy system on 27 April 1917, while the first convoy sailing set sail on 10 May that year from Gibraltar. And later that month, regular transoceanic convoys were established, and sinkings by U-Boats decreased dramatically, and didn't reach above 500,000 tons per month after that. Also, more U-Boats would be tempted to attack these convoys, leading to Allied Naval ships, which are guarding these convoys, have more chances in taking down submarines, which they have.

Depth Charges British Admiral of the Fleet Callaghan had first asked for these weapons to be developed in 1914. By 1916, an effective 'type D' had been successfully developed and deployed by the British Navy. These early anti-submarine crafts, however, only carried two depth charges. The first successful sinking of a U-Boat using a depth charge came on 22 March 1916 by Q-Ship Farnborough. However, depth charges were still very primitive and did not inflict a lot of damage on the German U-Boat fleet.

END RESULTS OF THE U-BOAT CAMPAIGN
Merchant Shippings sunk by U-Boats:
 * ~ Month ||~ 1914 ||~ 1915 ||~ 1916 ||~ 1917 ||~ 1918 ||
 * January ||  || 47,981 || 81,259 || 368,521 || 306,658 ||
 * February ||  || 59,921 || 117,547 || 540,006 || 318,957 ||
 * March ||  || 80,775 || 167,097 || 593,841 || 342,597 ||
 * April ||  || 55,725 || 191,667 || 881,027 || 278,719 ||
 * May ||  || 120,058 || 129,175 || 596,629 || 295,520 ||
 * June ||  || 131,428 || 108,855 || 687,507 || 255,587 ||
 * July ||  || 109,640 || 118,215 || 557,988 || 260,967 ||
 * August || 62,767 || 185,866 || 162,744 || 511,730 || 283,815 ||
 * September || 98,378 || 151,884 || 230,460 || 351,748 || 187,881 ||
 * October || 87,917 || 88,534 || 353,660 || 458,558 || 118,559 ||
 * November || 19,413 || 153,043 || 311,508 || 289,212 || 17,682 ||
 * December || 44,197 || 123,141 || 355,139 || 399,212 ||  ||
 * Total || 312,672 || 1,307,996 || 2,327,326 || 6,235,878 || 2,666,942 ||

Grand Total Sunk: 18,851,000 tonnage sunk 
 * ~  ||~ 1914 ||~ 1915 ||~ 1916 ||~ 1917 ||~ 1918 ||
 * On hand || 24 || 29 || 54 || 133 || 142 ||
 * Gains [//[|clarification needed] //] || 10 || 52 || 108 || 87 || 70 ||
 * Battle losses || 5 || 19 || 22 || 63 || 69 ||
 * Other losses ||  || 8 || 7 || 15 || 9 ||
 * Years end || 29 || 54 || 133 || 142 || 134 ||

Total Operational U-Boats: 351 Total Sunk in Combat: 178, 50% of U-Boats Total U-Boat Crew Member Deaths: 5,000