The Otranto Barrage

The British chronology of the war records under 1 October 1918 the establishment of an Allied net barrage across the Strait of Otranto, between the “heel” of Italy and the coast of Albania and Greece. This was the fixed barrage: a belt of anchored nets with explosive charges, which was to close to German and Austro-Hungarian submarines from Cattaro and Pola the route from the Adriatic into the Mediterranean. The sources do not agree on the exact date of its completion. According to the French historian of the war in the Adriatic, Auguste Thomazi, construction was resumed in February 1918 and finished five months later. The British official naval history (Newbolt), on the other hand, writes that in September the barrage was “nearly complete”.

A sieve across the mouth of the Adriatic

From the autumn of 1915 the strait had been watched by British drifters, armed fishing boats towing light indicator nets. The so-called Otranto Barrage effectively kept the Austro-Hungarian surface fleet in the Adriatic, but submarines passed through it almost unhindered. The strait is about 75 km wide and in places several hundred metres deep, and the drifters were easy targets for night raids. The largest of these, on 15 May 1917, cost the British fourteen drifters. The French and Italians had long believed that a fixed barrage was needed instead of mobile patrols. The first sections of it were laid in the autumn of 1917, but according to Thomazi storms destroyed them within two months.

In the spring of 1918 the Allies pursued two projects in the strait at once. The British admiral Somerset Gough-Calthorpe, commanding in the Mediterranean, relied on massed patrols. From mid-April submarines lay in wait off Cattaro, destroyers cruised in the middle of the strait, and in its narrowest part there were trawlers with hydrophones and lines of drifters. About a week later the French began laying a fixed net from the islet of Fano (Othonoi), north-west of Corfu, to the coast near Otranto. It was laid piece by piece, as the work was laborious and dependent on the weather. According to Thomazi the barrage was 66 km long and consisted of net sections of about 300 metres, suspended from buoys at depths from 10 to 60 metres and anchored to the bottom. Explosive charges were attached to the nets, which went off when a submarine became entangled.

Results

The barrage became a target for the Austro-Hungarian fleet. In June 1918 Admiral Miklós Horthy intended to strike it with almost all his battleships, but the sinking of the Szent István forced him to call off the operation. The only certain victim of the net recorded by the British official history was the German UB-53. On 3 August 1918 she ran onto two of the barrage’s mines and sank. Ten men were killed and 26 were rescued. According to the official history, however, the French and Italian admirals believed that the net still needed to be supplemented by deep minefields further north. In September the Allied Naval Council agreed in principle to the laying of such barrages in the southern Adriatic and off the Dardanelles.

The barrage was completed just as the war in the Mediterranean was coming to an end. At the end of September Bulgaria left the war, and at the end of October the German submarines began to leave their Adriatic bases to return home. They had to pass the fixed barrage in the Strait of Otranto and the mobile one in the Strait of Gibraltar. Most of them got through. By most assessments the Otranto barrage never closed the way to submarines, although at the end of the war it made their passage harder than ever before.