The Mark I directional hydrophone was designed at this establishment in 1917, and other exceedingly valuable work was carried out there connected with the detection of submarines.
At Malta an experimental station, with a hydrophone training school, was started in the autumn of 1917, and good work was done both there and at a hydrophone station established to the southward of Otranto at about the same time, as well as at a hydrophone training school started at Gallipoli at the end of the year.
"OTTERS" AND PARAVANES _The "Otter" system_ of defence of merchant ships against mines was devised by Lieutenant Dennis Burney, D.S.O., R.N.

(a son of Admiral Sir Cecil Burney), and was on similar lines to his valuable invention for the protection of warships.

The latter system had been introduced into the Grand Fleet in 1916, although for a long period considerable opposition existed against its general adoption, partly on account of the difficulties experienced in its early days of development, and partly owing to the extensive outlay involved in fitting all ships.
However, this opposition was eventually overcome, and before the end of the war the system had very amply justified itself by saving a large number of warships from destruction by mines.

It was computed that there were at least fifty cases during the war in which paravanes fitted to warships had cut the moorings of mines, thus possibly saving the ships.
It must also be borne in mind that the cutting of the moorings of a mine and the bringing of it to the surface may disclose the presence of an hitherto unknown minefield, and thus save other ships.
Similarly, the "Otter" defence in its early stages was not introduced without opposition, but again all difficulties were overcome, and the rate of progress in its use is shown in the following statement giving the number of British merchant ships fitted with it at different periods of 1917: By July 1, 95 ships had been fitted.
By September 1, 294 ships had been fitted.
By December 1, 900 ships had been fitted.
The system was also extended to foreign merchant ships, and supplies of "Otters" were sent abroad for this purpose.
A considerable number of merchant ships were known to have been saved from destruction by mine by the use of this system.
DEFENSIVE ARMING OF MERCHANT SHIPS The _defensive arming_ of merchant ships was a matter which was pressed forward with great energy and rapidity during the year 1917.

The matter was taken up with the Cabinet immediately on the formation of the Board of Admiralty presided over by Sir Edward Carson, and arrangements made for obtaining a considerable number of guns from the War Office, from Japan, and from France, besides surrendering some guns from the secondary and anti-torpedo boat armament of our own men-of-war, principally those of the older type, pending the manufacture of large numbers of guns for the purpose.