The Otranto Barrage was initiated in early 1915 to contain the powerful Austro-Hungarian navy (k.u.k Kriegsmarine) in the Adriatic, and particularly to prevent incursions against Allied maritime operations in the Dardanelles. In these early days of anti-submarine warfare, the Barrage consisted of a line of trawlers across the 45 mile (100 km) wide Otranto Strait, each vessel carrying nets intended to capture enemy submarines by entanglement.
While the overwhelming superiority of the heavy units in support was sufficient to deter an offensive by k.u.k Kriegsmarine surface ships it did little to stop their submarines, which remained a threat throughout the war. In addition, the Austrians mounted occasional surface raids on the Barrage itself, the most serious occurring on 14/15 May 1917 when 14 trawlers were sunk. The obvious answer was a close support force, but there was a chronic shortage of destroyers and light cruisers due to higher priorities in the Mediterranean and elsewhere.
Given this need and the apparent quietness of the Australia Station at that time, the Admiralty requested release of one division of the Australian Torpedo Boat Destroyer Flotilla for service in European waters. In return for the promise of an additional British cruiser for trade protection on the Australian coast, the government agreed to the despatch of the whole Flotilla.
Refitting of the First Division (Parramatta, Yarra and Warrego) immediately began at Sydney, while the Second Division - Huon, Swan and Torrens - which had been patrolling in the Malay Archipelago was refitted at Singapore. The six ships rendezvoused at Cocos on 7 July 1917, the first time the whole Flotilla had been assembled; Commander W.H.F. Warren RAN took command and, sailing via Diego Garcia, the Seychelles and Aden, the destroyers arrived at Port Said on 9 August. Here they picked up a convoy for escort to Malta, this trip providing great excitement for men used to the dreariness and monotony of patrol work in a naval backwater. The convoy reached Valetta on the 21st, but not it had encountered - and fought - a pack of at least four enemy submarines, one of which was sunk by Parramatta.
At Malta the Australian ships refitted again, then worked up during August and September. Even during this training and exercise period there were occasional alarms, such as rushing to the aid of a threatened convoy. One amusing incident occurred when the Flotilla sighted a surfaced submarine disguised as a schooner - it escaped after a depth-charge attack by Swan, but had been forced to dive so quickly it left its masts and sails on the surface!
Early in October, the ships moved to Brindisi (on the 'heel' of Italy), which was to become their base during their time on the Barrage. The actual patrol work began on the 14th, each division alternating between sea and harbour on a four-day cycle. The destroyers patrolled north of the minefields and lines of drifters, the idea being that they would both protect the drifters against enemy raids, and force any submarines encountered on the surface to dive so they would run onto the mines or become entangled in the drifters' nets while submerged. This put the Australian ships in a somewhat exposed position given that (in the words of the Official Historian) "the Austrian ships were more numerous, more heavily armed, and swifter than ours, their aircraft were busy and adventurous, and they had a habit of setting afloat drifting mines whenever a north-east wind was blowing."
The Flotilla was kept busy, escorting convoys, patrolling, dodging torpedoes and chasing the submarines that fired them, and destroying floating mines. In the early days submarine sightings were numerous but, as time went on, the U-boats became fewer and the time at sea became more routine. However, occasional incidents such as going to the rescue of the Italian troopship Orione and repelling a raid on the Barrage by five Austrian destroyers helped to break the monotony.
During their refits in the Mediterranean, the Australian ships were gradually fitted with the latest in anti-submarine equipment - rails or chutes for their depth-charges, hydrophones for underwater listening and balloon winches in place of the after torpedo tube. The latter were for streaming captive balloons and with them the basics of submarine 'hunter-killer' techniques (perfected by the Atlantic escort groups 25 years later) were worked out. Observers would be sent aloft in the balloon to spot for submarines below the surface; when one was sighted, a second destroyer was called up to drop depth-charges over the spot while the occupants of the balloon ensured the U-boat did not take evasive action or escape undetected.
As military activity increased in the Mediterranean and more resources became available, the Allied naval force assigned to the Barrage was also increased; by April 1918, it comprised 35 destroyers, four torpedo boats, eight submarines, six sloops, 52 trawlers, 74 drifters, 31 motor launches and 36 American submarine chasers. The Australian ships thus became a small component of this armada, and were absorbed into the British 5th Destroyer Flotilla. Nevertheless, a heavy workload remained and sickness, food shortages (the ships were allocated land near Wallaby Trot to grow vegetables) and the Flotilla's lack of reserve or replacement personnel all took their toll. Conditions were hard but casualties were remarkably light; unfortunately they included Commander Warren (drowned in Brindisi harbour in April 1918) and five members of Huon's ships' company killed in a fortnight by the influenza pandemic sweeping Europe later the same year.
The ships of the Flotilla began leaving the Barrage for the Aegean in October 1918 as the Dardanelles once again became a focus point. Subsequently, they were deployed to the Black Sea before going to the UK for refit, after which they sailed for home via Malta (where those which had lost their third torpedo tube had it restored), Port Said, Aden, Colombo, Malacca and Singapore. Darwin was reached on 26 April 1919 and, finally, Sydney on 22 May after an absence of two years and nine months.
Note:
The Australian "River" class destroyers were modified, slightly smaller versions of the Royal Navy's "I" (or "Acheron") class with the following specifications:
Displacement: 700 tons
Dimensions: 250 x 24½ x 9 ft (76.2 x 7.46 x 2.74 m)
Machinery: Parsons turbines; 3 shafts; 10,000 shp = 26 kts
Armament: 1 x 4-in (102-mm), 3 x 12-pdr; 4 m.g.; 3 x 18-in (457-mm) T.T.; depth charges
Complement: 66
The first pair, Parramatta and Yarra, were built in Scotland 1909-1910 and steamed out to Australia. Warrego was also built in the UK, then dismantled and shipped in sections to Australia; her re-assembly gave local workers valuable experience which they later put to use building Huon, Swan and Torrens (all Cockatoo Island, 1913-16).
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