Robert
The basic problem with the Type VII, IX, and even the newer type XXI boats was that they were basically surface craft with a limited underwater endurance. Fitting them with the advanced detectors we have today would not have overcome this basic characteristic of those boats. No matter what, they had to return to the surface about every 24 hours more or less to replenish air supplies and charge batteries. The anti-submarine tactics were designed to take advantage of this need for air. Actually, the U-boats highest success rate came during that period of the war when they had essentially unlimited access to the surface of the ocean with freedom from detection. The usual tactic during that period was for the U-boat to run at high speed on the surface (and they were relatively fast on the surface - just look at the hull design ) to get into attack position. Depending on the target and whether or not it was escorted the U-boat would then submerge to periscope depth, develop the firing solution, and fire torpedoes when the target came into range. During the very early stages of the war where they did not have to worry about aircraft, many U-boats attacked on the surface and sank their targets with gunfire in order to save the expensive torpedos.
Two Allied technical developments changed all this; (1) the development of airborne radar, and (2) the HuffDuff network. Once these two developments went on line there was no place the sub could go to be free of detection and attack. The HuffDuff stations could develop the position of a U-boat whenever it transmitted by radio - and the U-boats did a lot of radio transmitting. The accuracy of the "fix" on a U-boats position varied greatly depending on a lot of factors but it was generally accurate enough to vector ships and aircraft into the subs general position where it could be searched for by radar and/or sonar. Once the presence of a submarine had been determined and the "hunt" began the submarine had little chance. Forced to remain submerged, the submarine lost its mobility and was forced into evasive actions until it ran out of battery and/or air. Once forced to the surface the U-boat only rarely escaped.
Allied developments in improved weapons such as the "hedgehog", larger fast sinking depth charges, rockets, sonobuoys, and the "Fido" homing torpedo served mainly to increase the "kill rate" but the submarine had to be found and localized before these weapons could be used.

It was the fact that the WWII submarine was an "airbreather" which was its undoing and the addition of improved detectors would not have changed this basic fact. And that is also why the modern submarine is such a deadly weapon - it doesn't have to come to the surface and thereby reveal its position.
Hope this is usefull to you.
Don B