Letter from WSC to Sir Robert Renwick marked "Secret" stating: that it has just a year since he charged him to make and distribute H2S instruments [device to guide bombers using ultra short waves] into the service as soon as possible and that now 2 squadrons had been fitted and that there were now 700 instruments; that this apparatus had increased the accuracy of bombing: that it will become more important as the radius of operations is extended; that its later developments Fishpond and A G L I will reduce bomber losses and that he was anxious that he should speed up the improved H2S at all costs Signature in typescript. Copy.