Images - Visual Indicating Equipment

VIE: The acoustic “radar” that taught Britain to read a screen

Long before British radar operators watched coastlines sweep around a PPI scope, a small EMI team led by Alan Dower Blumlein was teaching anti-aircraft crews to seesound. Their 1938 invention, VIE—Visual Indicating Equipment—took the familiar acoustic sound-locator (big horns on a carriage) and added a cathode-ray tube, turning the fuzzy business of listening for engines into a visual bearing-and-elevation readout. In effect, it brought the culture of screen-based gunnery to Britain just as war loomed.

Origins: stereo ideas meet air defence

The immediate spark came in June 1938, when EMI engineer George Condliffe suggested borrowing part of Blumlein’s binaural (two-channel) stereo mathematics to indicate the direction of a sound source. Blumlein and colleagues ran quick tests, then formalised the method: feed two microphones from a single reflector into sumand difference channels, and display the result visuallyon a CRT so an operator could centre the target with confidence. The Air Ministry saw a demonstration that October and placed orders: EMIto supply the indicator and CRTs; Standard Telephones & Cables (STC)to provide the microphones.

Blumlein codified the approach in an internal note—Principles of EMI system of sound location(10 Oct 1938)—explicitly replacing headphone “golden ears” with an objective screen. That shift, from aural judgement to a screen-drivenbearing, is where VIE foreshadows radar’s operator ergonomics.

How VIE worked (and what it used)

VIE piggy-backed on an existing acoustic sound locator: two microphones sat in a parabolic basket, their outputs combined into sum(average level) and difference(left-right imbalance). The operator watched a small CRT whose trace and scale made the “zero-in” point obvious; pedals and switches selected base length and functions. The Air Ministry had already standardised on the STC 4021C—the military version of the famous “apple & biscuit” microphone—so Biggin Hill loaned early sets while EMI focused on the indicator.

The 4021 series itself was a rugged moving-coil microphone widely used in broadcasting and measurement, exactly the sort of stable, predictable transducer a visual system needed. For the display tube, EMI drew on its television bench: contemporary accounts even note the Emiscope 4/1three-inch CRT “used on visual-indication equipments (V.I.E.) in the early stages of the war.”

From prototypes to the field

By late December 1939 EMI had completed six VIE prototypes, having wrestled with CRT supply (a push that led EMI to manufacture its own tubes). In mid-January 1940, installer Westlake fitted the first sets near Horfield/Horsfield, Bristol. The winter was brutal—ice formed on the indicator window—yet VIE “worked well,” convincing sceptics in both industry and the Air Ministry. EMI’s reward was a production ramp that saw over 400 sound-locator setsequipped with VIE by year’s end.

Some of the most telling feedback came from Gunnersbury Parkin West London, where ground-staff trained on VIE. Blumlein, who lived nearby, would stroll over at night to talk with the crews about what helped, what didn’t, and what should change. It was hands-on, iterative engineering in the middle of the Phoney War. Gunnersbury was one of London’s heavy AA batteries (site ZW11 in the Inner Artillery Zone), a natural home for a tool that promised faster, less ambiguous bearings to pass to searchlights and 3.7-inch guns.

What an operator saw

On the carriage, the front endstill looked like inter-war listening gear—horns or a reflector—but the VIE boxadded a compact oscilloscope-type indicator, bearing/elevation amplifiers, a junction box, and simple foot controls. Instead of arguing over where the drone of a Junkers seemed loudest in headphones, a crewman centred a trace on the CRT’s scale and called out the number. The practical payoff was speed under pressure—and, crucially, training thousands of operators to trust and act on an electronic display.

The bridge to radar

VIE wasn’t radar; it listened, passively, to engine and airframe noise. But it prepared the ground. By acclimating AA crews to screen-centricoperation and by hardening EMI’s supply chain for CRTs and indicators, VIE smoothed the jump to radio-based gun-laying systems. In fact, the VIE work lit a spark for Blumlein and colleague Eric White: almost simultaneously they began a 60 MHz “GU” gun-laying radar, with multiple aerials and a CRT display to extract bearing, range, and altitude—an early EMI entry into active RDF.

The lineage also ran through hardware. The domestic TV research that made small Emiscope tubes practical helped ensure that when radar arrived—first at metre-wave, then at centimetric wavelengths—the indicator side of the house was ready. Contemporary electronics writers could casually mention the Emiscope 4/1’s wartime service on VIE when repurposing surplus parts for lab oscilloscopes—quiet proof of how a pre-war TV tube became a gun-crew’s aiming aid and then a peacetime instrument.

Scale, limits, and significance

Seen against the tsunami of radar that followed, VIE was modest: a few hundred add-on kits, fitted to acoustic locators that would soon be out-classed by CHL and GL radar. It also had the intrinsic limits of acoustics—range and accuracy shrank with wind, temperature gradients, and the chaos of Blitz nights. Yet in 1939–40, when radar coverage was still patchy and training pipelines were just forming, VIE delivered a real operational gain: faster, more repeatable bearings, especially for searchlight control, and a vital cultural shift toward visualisedfire control.

It also stands as a quintessential Blumlein project. The mathematics and circuits came straight from his stereo work—sum/difference logic; rigorous attention to phase—and the execution leaned on EMI’s television expertise with small CRTs and clean operator layouts. Above all, it shows Blumlein’s habit of walking out to the emplacement, talking with users, and iterating. That same pattern would carry into his later, far more famous work on H2S, where the display again made the difference between theory and a tool crews could fly by.

A concise legacy

If you strip VIE to its essence, it did two things brilliantly at exactly the right moment. It translated stereo into gunnery, and it trained a generation to read a scope. In doing so, it bridged Britain’s inter-war world of horns and human judgement to a wartime universe of electrons and phosphor, where the surest path to a target was the one you could see.

DORA MEDIA PRODUCTIONS

Images - Visual Indicating Equipment