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plot a line on a map of the locality, yielding one bearing on the source. The pilot would then use a compass board (war-surplus submarine gear) to direct the driver to a second point, from where a new readingwould be taken; and then to a third. These three readings together identified a triangular region about two hundredyards on each side, which operators came to call the "cocked hat." At this stage the van would proceed to the edge of this triangle and begin "combing out" - that is, repeating the triangulation procedure to isolate a single stretch of road. Finally, by driving down the road slowly the operator might even identify the actual house from which the oscillation issued. The men could then knock on the door of the "howler" to inform him or her of the antisocial behavior.

FIGURE 13.11. The suspected oscillator suffers ostracism. BBCHandbook (r929), 352.

FIGURE 13.12. "Detectives locating an oscillator."BBC Handbook (1929),350-

FIGURE 13.13. "Now then, where's that crystal set?" Daily Express, February 16,1925-

The BBC identified the region around Windsor as agood testing ground for the technology. A Commander Carter had already done local investigatory work, and he helped the London team with the lay of the land. On December 21 the van drove down from the capital. After much initial frustration, it did eventually succeed in identifying a perpetrator. The first ever victim of a detector vanwas aMiss Pritchett of Slough. Whether this was such agreat triumph could be doubted, however: she lived in the same street as the person who had complained of interference, so "detecting" her by conventional means would have been straightforward. Moreover, she was not apirate. Her set was licensed, but had simply never been properly adjusted. So the test did nothing to show the worth of the vehicle for identifying a serious oscillator, let alone apiratical one. And the expedition culminated in a minor accident that put the van out of action for weeks.

Nonetheless, a milestone of sorts had been reached, and a public demonstration was soon scheduled. It had to be carefully stage managed, since the van could only localize a source of oscillation if the interference persevered for several hours while it trundled through the streets performing its triangulation. Most real listeners-in, needless to say, were not obliging enough to leave their radios on for so long. A member of staff therefore quietlyvolunteered his house in North London for the carefully rehearsed event. None of this was revealed to the press, which treatedwhat it saw on January 17 as a genuine detection. Representatives of the Press Association, Central News, and Reuters traveled with the van as it drove north from Aldersgate Street and followed the procedure for tracking down an interferer. When it zeroed in on the suburban house from which the howl originated, the journalists were duly impressed and hailed a revolutionary advance. Newspapers across the nation echoed their enthusiasm. A "wonder car" had arrived, they announced- a "Sleuth Van which Cannot Fail." The Post Office had "declared war, scientific war, on allwho oscillate," declared the Y rkshire EveningPost, reporting that the van would replace the monitoring oflocal enthusiasts. Perpetrators were dulywarned that the "oscillation war" (as the Western Mail called it) could now have only one winner. "The effect is as good as ifwe had entered the house," the van's engineer was quoted as saying. Most howlers were unaware of their offense, newspapers were careful to point out, and welcomed being told of it when they were detected. Three cases of such ignorance, all of them women, were widely reported (fig. 13.04).

FIGURE 13.14. Post Office van for detecting oscillators. BBC Handbook (1928), 184•

With this success under its belt the Post Office proceeded to inaugurate its second detector van in the Manchester area in mid-1927. Two years after that a third followed. How successful they really were is rather unclear. Some oscillators were certainly detected, but very few were deemed worthy of more