'ASV Recorder' [Air to Surface Vessel], R H Brown Typescript memoranda regarding ASV recorder and warning system, with circuit diagrams. Also contains an offprint on the electronic recording of weak electric currents, by F E Ludkin. The object of the ASV recorder was to produce a permanent record of echoes detected by the ASV apparatus. The ASV warning system, which was meant to warn the operator of the presence of an echo, had not reached a practical state of use. 1941