B&N Mobil Directo

The **Mobil Directo** (sometimes styled as **Mobil-Directo**) was a rotational civil defense siren, made by Biersach & Niedermeyer Co. from 1942 until 1967, and was the predecessor of ACA's Allertor 125. It was one of the earliest rotational sirens ever created, and boasted unparalleled sound output when it was released, and found extensive use throughout the United States and Canada.

## History and Design

The Mobil Directo was created in the early 1940s by Biersach & Niedermeyer Co, a steel company that had been in business since 1873, founded by Louis Biersach and August Niedermeyer. The company was contracted by the American government to create a high powered air raid siren that would be suitable for use in both the domestic market as well as in the Pacific Theatre. The original gas-powered Mobil Directo would be finished and began production in 1942, using the then-new design principle of a directional, rotational siren. Later in 1948, after the success of the gas powered variant, an electric variant would begin production. A dual tone chopper would also be introduced.

The Mobil Directo uses a unique split intake/projector design that was later carried over to the Allertor. The bottom horn is the intake, where air is drawn in through the chopper located inside the projector drum, and the sound comes out of the large top horn. The drum serves to compress the sound and air, which is then forced out of the top projector horn through an L-bend. The siren's external dual-sided motor (or engine) drives both the chopper as well as the rotator. The rotator is belt driven from the motor/engine, using two belts connected to a gear reduction drive that drives a single powered wheel and two unpowered wheels to rotate the entire siren unit at once. On BN52 and BN54 units, the gasoline engine drives the chopper and rotator in the exact same fashion.

Something to note on all Mobil Directo sirens is that the chopper spins the same direction as the rotator does, with both being configured by default to spin clockwise. Due to the bidirectional rotor and stator of the siren, it does not matter which way the siren spins, it will be equally as loud regardless. This applies to both 8 and 10/12 port units.

B&N's siren division went bust in 1967 as sales waned, which brought the production of Mobil Directos to an end after a 25-year production run. B&N's siren division then reformed itself into Alerting Communicators of America, partially reusing the design (rotor, stator and projector) for the ACA Allertor 125. Today, Mobil Directo sirens (the gasoline-powered ones, especially) are very rare, as most have been removed since the end of the Cold War, and/or replaced with newer sirens. Only three units still remain in service, one converted BN52 and two BN44E units, but the vast majority of remaining units sit silently, rusting away on their poles, a forgotten reminder of the perils of the Cold War. A privately owned BN52 unit is currently undergoing restoration by Jerry Wick and is currently the only operational gasoline-driven unit in existence.

## BN52 and BN54

This was the original variant produced, introduced in 1942. The gasoline-engine driven BN52 (and later BN54) Mobil Directo used a 25 horsepower, VF4 Wisconsin air-cooled gasoline engine to drive the rotor/stator assembly while also rotating the entire siren assembly. This variant was initially produced for the U.S Army for use on remote island airbases in the Pacific Theatre during World War II. In the 1950s, during the height of the Cold War, the BN52/BN54 were installed in several cities and towns throughout the United States, especially in California. Approximately 2000 gasoline powered units were produced and sold until its discontinuation around 1953. All BN52 and BN54 units came exclusively in 8-port single tone and were rated at roughly 125 dB at 100ft. This rotor was sourced from Federal Electric/Enterprises, and is the same rotor used in 8-port C3 1/2 Fedelcode sirens. Due to how the engine only supports the rotor on one side, an additional spider bearing is added inside the intake, held up by three supports. The rotation gearbox on the siren is configurable, with off, low, and high-speed rotation settings. When the engine is idling, the siren is capable of rotating without sounding off when set to "low" or "high", something an electric unit is incapable of.

This variant of the siren was designed to be able to operate independently of grid power, which made it particularly useful in areas where electric power was either unreliable, not readily available, or in areas where grid power would likely come under attack. The siren could be operated by an operator physically using a switch on the rear of the siren, who would effectively ride the siren as it rotated, or could alternatively be started and ran remotely using a remote throttle switch. This design concept would be used in several other sirens such as the Thunderbolt 2000 and the Chrysler Air Raid Siren, although this practice fell out of favour by the mid 1950s.

    The only visible difference between the two models are minor engine differences. One example of a BN52 remains in service in Milwaukee, WI, which had been converted to using an electric motor in the 1980s, while another privately owned unit is currently undergoing a full restoration and is operational. Two operational units exist, one in San Bernardino, CA (inactive but is apparently operational as of roughly 2015) and the aforementioned privately owned unit, which was restored by Jerry Wick.

## BN44E

The second variant, the electric-motor driven BN44E, was introduced in 1948. This variant retained the same components, but instead used a dual-sided 10-horsepower Louis Allis AC electric motor. Canadian units used a different 10HP motor manufactured by the General Supply Company. The two variants were offered alongside each other until the discontinuation of the gasoline-powered variants in 1953. The electric variant continued to be produced until around 1967, when it was discontinued after B&N went out of business and reformed into ACA. The BN44E was available in both 8-port single tone, as well as 10/12 port dual tone. 10/12 was the most common version installed. Some 8 port single tone units are also former BN52/BN54 gasoline units that were converted. Two examples of a BN44E remain in service, an 8-port model in Memphis, TN and a 10/12 model in Pottsville, PA with a replacement projector. The rotor and stator of the 10/12 BN44E would later be reused for the 10/12 port 1st generation ACA Allertor 125 in 1968, as well as the 10/12 variants of the ACA Banshee 110 and Screamer S-10.

## References

1. ↑ Though not the first, as that title likely belongs to Swedish Electric Co.