13 April 1917 – Spider’s Web

Since the declaration of unrestricted submarine warfare back in February one of the main concern of the Navy has been to protect shipping in the English Channel supplying the forces in France. The German U-boats appear to have stepped up their campaign in April with an average of 20,000 tons a day lost.

The Admirality has had no option but to introduce a convoy system to protect shipping. However this will take time to set up and in the meantime various seaplane stations around the coast have stepped up their patrolling.

In an effort to improve the detection of u-boats, the Felixstowe flying-boat station has developed a more systematic approach.

It was known that many of the U-boats, on the way to their hunting grounds, passed near the North Hinder Light Vessel which was used as a navigation mark. Moreover, in an effort to conserve their battery power, most passed the area on the surface.

IMG_0925.PNGA search pattern was therefore devised to allow for the efficient searching of the area around the Light Vessel, which became familiar as the Spider-Web.

The web, centred about the Light Vessel, was an imaginary octagonal figure, sixty sea miles in diameter. There were eight radial arms (each thirty miles long), and chords, joining the arms, ten, twenty, and thirty miles from the centre.

The web enabled about four thousand square miles of sea to be searched systematically. Under normal conditions one flying-boat could search two complete sectors, enclosed by the arms, or a quarter of the whole web, in five hours. Today the first missions were flown using the new system.

As time went on the system was refined by plotting the latest known movements of u-boats to allow searched to be focussed in those areas.

Similar search patterns were introduced around the coast wherever u-boats were known to operate.

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