Question about V2s and English defences

First post here.

I seem to recall reading that in WWII, the government employed people who could see into the near ultraviolet to watch for V2 exhausts at night.

Is this likely? Did the V2 exhaust emit UV light sufficiently brighter than it emitted visible light to justify this? Was it true?

Thanks a lot.

Memory has probably played you false. V2 rockets had next to no exhaust when descending. They burned all their fuel on the way up their trajectory.

The V1 (an unmanned aircraft powered by a ramjet) emitted a hot exhaust, of course

Cheers and all,

V2 was a ballistic-trajectory weapon - which means that on the downwards leg of its trip the fuel was long-since exhausted and the engines firmly off. The only time that you could see the exhaust would be on the upwards leg, when it would have been kind of obvious, but that wouldn't tell you much about where it was going to land. It's possible that the passage of a large supersonic object through the high atmosphere might have produced briefly enhanced airglow (from compression regions driven by shocks) but you'd not detect that without some really good photomultipliers - which didn't exist until English Electric started making 'em in the '50s (that valve is still the best airglow detector, I believe - shame there aren't many left...). The only way of detecting V2s was before launch or after landing.

This sounds completely bogus.

First, even if a V-2 exhaust could be sighted, what good would it do? The British had no weapon capable of interfering with a V-2 in flight.

Second, there would be only seconds or at most minutes between the sighting and impact, so there would be no time to do anything.

Third, the V-2 was a 'ballistic missile'. That is, once its fuel was exhausted in boost stage, a V-2 followed whatever trajectory it was on at that moment till it hit something, just like a rock flung from a catapult.

The V-2 used all its fuel in the boost stage, to establish a trajectory that would hit the target. After that it had no exhaust to be spotted.

The question you have to ask yourself, So what? Since the V-2 travelled faster than any possible defence available,so what if they could see the exhaust? There was precious little they could do. Remember we are still trying to perfect an effective anti-missile defence today, 60 years later. Even if you can see the exhaust, the lead time before the V-2 impacted was very small. Too small to make an air raid warning effective. And all that would do was put everyone into a shelter all the time. Better to just accept the damn things were coming and try to stop them at the source. On looking at it, it may have been a propaganda ploy. If you tell the people there are watchers looking out for the V-2's then the people might think you are at least doing something. Even if that was absolutely nothing. My 2c

I don't know about the last point, but physiologically it is plausible. Cells in the retina are capable of detecting light just into the UV range, however most UV light is absorbed in the lens of the eye hence most of us cannot 'see' UV.

People who have had their lenses removed ('couched' - most commonly due to cataracts - can detect UV. I beleive these days the modern replcement lenses in common use absorb this UV and, I would imagine during the war, the thick spectacles required by someone with no internal lens (aphakia) would also pretty much eliminate this 'advantage'.

Without spectacles the world would obviously be very blurred, but I suppose it might be possible for an aphake to broadly locate a source of UV or one might speculate on the use of special UV transparent spec's. Whether the V2s emitted sufficiently in the near-UV range is yet another matter.

Cheers

Ken Cocker Ophthalmology, Imperial College

It was not the V2 but for reading an infared signal device. I am not sure if it was SOE or some other group.

It sounds like disinformation - a false story deliberately put about at the time to try to disguise the truth. This one sounds very similar to the one about night fighter pilots eating carrots to improve their eyesight, which was put about when airborne radar started to be used on their aircraft.

The Chain Home radar system was the earliest of our coastal radars and was very inefficient. One of the reasons for the inefficiency was that the some of radar waves were sent out in directions that were of no practical use. Nobody had any use for very high altitude radar, until the V2 rockets started coming over. They flew straight through one of the lobes of radar that, until then, had been considered wasted energy. It took too long to plot the trajectory from the radar for it to be possible to warn people of an attack, but it was possible to back-track with considerable accuracy, to pin-point the launch sites. This sounds like just the sort of story that might be invented to explain why there was usually a very short period between a V2 being launched and its launch site being bombed.

Colin Bignell

Trouble with this is that V2s were not launched from fixed installations. The V1 needed a concrete launch ramp, which could be bombed, thus the 'launch site' destroyed. But the V2 launched from a (portable) stand that held it vertical for as long as the countdown required. A barrage of V2s required a logistical organization (central supply, dispersal via launch trucks, etc.) but needed no 'launch sites.' You could launch one from any school playground or paved parking lot, perhaps a gravel parade square. Britain obviously wanted to know from where V2s had been launched, in order to counterattack: but the bombing targets identified with the help of such information were not the locations from which actual V2s had been launched.

landing.

According to R V Jones, of the 1115 V2s launched against London, about 65% were detected by radar in their ascent and their rough bearing ascertained. Civil defence in London and SE England was thus given a few minutes warning of many V2 launches and their probable area of landing. I also have a vague recollection of a ballistic missile warning radar system involving many hundreds of grid aerials being laid out in southern England which was capable of giving an accurate plot of the impact point of an approaching V2 with a few seconds notice.