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The Derry Yard
By Vance Crockett
(republished here with the permission of Waterside Voices, Derry)

I served my apprenticeship in the Derry Shipyard — 1941-1945 before going to sea in the merchant navy. I can only recall one ship being damaged by a u-boat and repaired in Derry and that was the HMS Londonderry, a sloop which had her stern badly damaged by an acoustic torpedo. This was a new type evolved to be attracted by the cavitation caused by propellers.
A woman scientist working in the yard at the time designed the counter measure to be fitted to high speed propellers ie. Royal Navy ships. It was never stated it was a secret so no one bothered to talk about it. Had it been ‘hush hush’ the German Ambassador in Dublin would have known about it within hours.
The parts lay about the dry dock. I was in the fitting shop at the time and had the job of drilling holes in the elliptical circular tubes. These were fitted forward of the propellers and compressed air was pumped through the holes to destroy the partial vacuum caused by the high revving warship propellers.
Merchant ship propellers were normally low revving and did not cause the large amount of cavitation required.
The U-boats were essentially employed to sink/damage merchant ships and rarely ever attacked Naval vessels. The acoustic torpedo was the only weapon used to attack warships. A lot of escorts were small corvettes which were slower than the u-boats who on the surface could outrun the corvettes. This was until frigates were introduced in the latter part of the war.
Sinking warships had no effect on the war. Sinking merchant ships did and they very nearly succeeded. Unlike ordinary torpedoes or shells which had to be accurately aimed, it was sufficient to release the acoustic torpedo roughly towards the stern of the ships and the fast revving propeller and the partial vacuum caused by it did the rest.
Destroyers, frigates and sloops were ideal targets for the acoustic torpedoes because of their high speed, 20 plus knots and fast moving propellers turning 180 revs per minute plus, creating the necessary cavitation.
Within months the lady scientist had solved the problem and the acoustic torpedoes were phased out by the Germans.
Initially American ships were repaired at the Yard, as they were almost new, very little was needed. Within a short time they had their own berths, behind fencing beyond the Yard, guarded by US naval sentries.
The fifty ‘old’ American coastal destroyers swapped for British bases abroad, by contrast were almost complete wrecks.
They had been laid up since WW1, and needed a great deal of servicing all the time they were in the service. The most effective one was the HMS Campbellian, which blew up the dock gates at St Nazaire. British warships were fairly old or had engines requiring constant servicing, usually corvettes with reciprocating steam engines.
The only Russian Naval vessels to reach Derry were a fleet of wooden motor launches, not even as big as British high speed torpedo boats. They were brand new from America and the Russians had sailed them across the Atlantic to everyone’s amazement, even the Admirality.
They stayed long enough to refuel and restore and off they went to North Russia, they were SEAMEN to their bootstraps.
In the final analysis, without the facilities at Derry during the war — Britain would have lost the war. Even with it we very nearly did, the merchant ship loses were so great

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