FIGHTING    THE   SECRET    WEAPONS

contact mines by E-boats after a preliminary aircraft attack on the sweepers. In these offensives the sweepers gave a good account of themselves, although there were inevitable casualties, including one trawler sunk with nineteen of her crew. But many aircraft were brought down. H.M.T. Berberis, who destroyed one and severely damaged another off the East Coast, received a signal of congratulation on her efficient gunnery from the Board of Admiralty, which also bestowed praise upon the whole Patrol Service in the Nore Command for its excellent spirit in the face of repeated air attacks. Nor was the campaign confined to the waters off the East Coast, for Dover, the Solent, the Bristol Channel, the Mersey and the Clyde were visited by minelaying aircraft. The Dover trawlers, besides being bombed and machine-gunned from the air, were under frequent shell-fire from the French coast.

The Admiralty's answer to this campaign was sweeping by night. This was unknown in the last war and it presented a complex problem, particularly in the tidal channels of the Thames Estuary. But it was mastered, under the pioneer leadership of Captain G. B. Hartford, D.S.O., R.N., and during the winter of 1940 the sweepers of one base covered 1,000 miles every week. The strain on officers and ratings was severe, and the work was not done without loss, but the casualties were far less than they would have been in daylight operations, exposed to air attack.

The result of the sweeping during the first twelve months of the war was an achievement of which the little ships could be proud, but for them there was no resting on their sweeps. From day to day there was no knowing what fresh " secret weapon " would confront them. None knew better than they that across the water the best brains in Germany were devising new engines of destruction, one of which at any moment they might have to meet.

In due course it came. Observers began to notice that minelaying aircraft would cut off

their engines before releasing their mines. There were reports of more unexplained explosions, some of them in water which had been swept for ground and contact mines. The new type was found to be actuated by the underwater sound emitted by the passage of ships through the water. This became known as the acoustic mine. Once again the experts of H.M.S. Vernon tackled the problem and took measures—which of necessity must remain secret—to counter the new campaign.

So the battle of brains goes on. It was certainly well for British shipping that the German claim to have sunk H.M.S. Vernon (in fact a shore-based establishment) was a Goebbels lie. While the Germans continue to produce their " ingenious variations," as Mr. Churchill has called them, the men of the Vernon continue to lay their counter-plans, deducing from their experience what the next trap may be, so that they may be ready when it comes and, if possible, at least one jump ahead in their precarious work of finding the right equipment to place in the hands of those whose duty it is to sweep the sea.

DEAD LETTER. The German message on the captured mine says : " Guide me on my way aright, then Churchill will be in sad plight."