SuperKraut,

According to the information i have the allies were actually developing their own 'array' sonars independently of the Germans.However the allies were applying 'array' technology to active sonars rather than passive sonars like the German GHG.The first array sonar developed by the allies was the post-war American QHB.

As in the GHG , a beam was formed by adding up the outputs of different elements with different phases.In this US array,the sonar was a cylinder of seperate staves (transducers).Each stave (transducer) was wired to a corresponding element in a scale model of the array.The appropiate phases were appilied by a commutator rotating around inside the model,connecting to a few staves at a time to the receiver.This commutator spun at 300rpm,thus in effect sampling all directions to seek echoes (the QHB 'pinged' in all directions simultaneously).Range was lost because the commutator could never pick up more than a fraction of the full echo from any given direction.Later versions were given additional commutators to put out directional beams for greater range.

The advantage of this 'commutator' technology is that the sonar opperator did not have to wait for a ping to come back from any given direction as the transmission and reception beams were no longer connected.With the old style 'searchlight' sonars the opperator had to turn the beam,'ping',listen for a return echo,and then move to the next bearing and 'ping' again etc,etc.This 'searchlight' mode was too slow to keep up with the type XXI and once the allies became aware of the type XXI's amazing underwater performance (from the losse-lipped Japanesse military attache to Berlin who radio'ed back details of the type XXI to Japan...the allies having long ago broken the Japanese diplomatic code),the development of active 'array' sonars to counter the type XXI began.The first fruits of this was the QHB sonar which came into service shortly after the end of WW2.

Only with the BQR-2 did the Americans addopt the 'array' principle for passive sonar and then they added their proven 'commutator' technology to it,in effect allowing BQR-2 opperators to listen in all directions at the same time.This was eventually feed to a 'Bearing-time recorder' the analog precurser of the modern 'waterfall' display,which is the way all modern passive sonars display
their data.

I hope this is useful SuperKraut

Rgrds

Sniper.