The development of both active ASDIC and passive sonar (SOund Navigation And Ranging) proceeded apace during the war, driven by the first large scale deployments of submarines.

U-517 then escaped destruction when it entered Forteau Bay and ran afoul of the corvette Weyburn, which was unable to get an asdic contact.

Submarines were slow while submerged, and ASDIC sets did not operate effectively at speeds of over 20 knots (23 mph; 37 km/h).

Submarines were slow, and ASDIC sets did not operate effectively at speeds of over 20 knots.

On January 13, 1943, Ville de Quebec was escorting a 15-ship convoy in the Mediterranean when asdic operator Stanley Mill reported a submarine presence on the starboard bow.

These tests proved the German designed submarines were, in 1936, practically immune to British anti-submarine weapons including Asdic.

On January 13, 1943, Ville de Quebec was escorting a 15-ship convoy in the Mediterranean when ASDIC operator Stanley Mill reported a submarine presence on the starboard bow.

We picked up a Japanese submarine on our ASDIC [Anti-Submarine Detection Investigation Committee] and we took evasive action.

The ships assigned to the FNFL in 1943 had in addition one 40mm gun and three 20mm AA of the American Oerlikon model and additional ASW launchers, as well as an ASDIC.

These tests proved the German designed submarines were, in 1936, practically immune to British anti-submarine weapons including Asdic.

It was the Southern Isles, Southern Maid, Southern Floe and Southern Sea : 350 tons former whalers equipped with one 4-inch gun, several machine-guns, one asdic and deep charges.

In September 1939, an ASDIC was added, their AA was revised, a platform added including 8 13.2 mm HMGs in two quadruple mounts in place of their central cannon.

The ships assigned to the FNFL in 1943 had in addition one 40mm gun and three 20mm AA of the American Oerlikon model and additional ASW launchers, as well as an ASDIC.

Subsequent sweeps over the area with the assistance of RNZS TUTIRA, USS ROWAN and also FMS LA GRANDIÈRE ASDIC teams, failed to re-established contact and the attack called off.

New radar and sonar (ASDIC) technologies helped the Allies find the U-boats and new weapons, like the “Hedgehog” bombs, helped sink the submarines more effectively.