The 'array' technology was first discovered by the allies when they captured U570. The reason this sub was renamed HMS GRAPH was the ammount of technical data the allies were able to extract from it.This sub showed the allies how far ahead the Germans were in some areas but also that they so far lacked a small radar to fit on the U-boats. The reason why the allies only used 'array' technology after the war was twofold:

1. Until the advent of the 'Shnorkel' countering U-boats was most effective by using radar technology (an area where the allies had a commanding lead over the Germans...always play to your strengths..)

2. Allied Subs had good radars and had target info passed onto them by the allies excellent crypto network. Long range search sonars were not as important.Also the areas were allied subs tended to operate (S.E asia,Norway.Med) have a reputation for having poor sonar conditions (due to thermal layers/heating effects).Long range sonars suffer serious degradation in these conditions.

It was also a question of resources. The allies had ploughed huge resources into radar and would need to put compareable resources into sonar development. The majority of the allies sonar experts were involved in developing homing anti sub torpedoes. Shortley after the end of the war the US introduced its first 'array' sonar the QHB (which was an active sonar...not passive like the GHG). The first passive array was the BQR-2 which was fitted to the 'Guppies'