Thanks for that Bruce, very interesting indeed. The RAF used these H2S and later H2SX sets on Halifaxes, Stirlings and pathfinder DH Mosquitos and, on reading up on the subject a very improbable but plausible reason for the H2S name as follows...
"The targeting radar was originally designated "BN (Blind Navigation)", but it quickly became "H2S". The genesis of this designation remains somewhat mysterious, with different sources claiming it meant "Height to Slope"; or "Home Sweet Home". The "S" might have also had some connection to "S-band", but it is plausible the abbreviation was deliberately obscure as a security measure. There is also a rumour that it was named after hydrogen sulphide (chemical formula H2S, in connection with its rotten smell), because the inventor realised that had he simply pointed the radar downward instead of towards the sky, he would have a new use for radar, ground tracking instead of for identifying air targets and that it was simply 'rotten' that he hadn't thought of it sooner! The "rotten" connection, with a twist, is propounded by R V Jones who relates the tale that, due to a misunderstanding between the original developers and Lord Cherwell, development of the technology was delayed, the engineers thinking that Lord Cherwell wasn't keen on the idea. Later, when Cherwell asked how the project was progressing, he was most upset to hear that it had been put on hold, and repeatedly declared about the delay that "it stinks". The engineers therefore christened the restarted project "H2S" and later, when Cherwell inquired as to what H2S stood for, no one dared tell Cherwell that it was named after his phrase—instead they pretended, on the spot, that it meant "Home Sweet Home"—which was the meaning that Cherwell related to others (including R V Jones)."