Ah, H2S - a wonder indeed. An all-British centimetric radar system conceived in the 1940s for target identification and navigation for bombers and only taken out of service half a century later when the last Vulcan was taken off active duty. It was used for the bombing run on Port Stanley airfield in the Falklands conflict. The Germans captured one of the early WW2 versions from a lightly crashed Halifax bomber and from it gleaned enough information to accelerate creation of their Wurzburg and Freya radar systems. Without that capture, they probably would have taken another couple of years to get to the same point. Unfortunately, the effectiveness of German night-fighters pursuing our bombers was increased considerably by the capture of H2S and the earlier use of Wurzburg and Freya systems.
The enabling technology for H2S was the multi-cavity magnetron as a source of high-power centimetric waves - the descendent of which powers your microwave at home. Although the magnetron was developed in parallel in a number of countries, it was the British who got it working first. It's a thermionic device, or "Valve" in old-fashioned language - but unlike other valves it has never been replaced with a compact transistor/semiconductor equivalent. There is still no semiconductor device that can produce centimetric or millimetric waves at such high power in a single device - hence why your microwave still uses one.
As the name suggests, it relies on magnetic fields, and extremely strong ones at that. Generally, a horshoe magnet is used with the valve placed in the intense field in the gap of the horseshoe. I have a number of old magnetron horseshoe magnets and you have to be careful to retain a keeper across the open gap, otherwise all the ferromagnetic bits on your bench race rapidly towards the gap (I kid you not). I once entered a radar workshop to see what appeared to be a 6 inch nail suspended in mid air... On closer inspection, one end of it was tied off to the bench with very fine fishing line and the nail was held in mid air by a magnetron magnet in a cupboard fully 6 inches away from the nail! A good illusion.
But nobody has ever been sure where the name H2S originated, or what it stood for.
Once you have started something there is no going back in Life.....