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The Primed Oscillator Expendable Transponder (POET), the AN/ALE-55 Fiber-Optic Towed Decoy, and Hot Brick - these three products led us to the electronic warfare technologies we have today. These technologies made a tremendous impact on aviation history, and are now featured as historic artifacts in the Smithsonian National Air and Space Museum, Steven F. Udvar-Hazy Center in Chantilly, VA, as part of the museum’s defense-military avionics collection.
Not your average POET
In the 1940s, the British started the defensive practice of throwing thin strips of metal, also known as “chaff,” out of the window of their aircraft. These metal strips confused enemy radars, causing them to see multiple reflections and lose track of the actual planes – a tactic that would come to be called “jamming.”
“We tried to come up with a concept that allowed us to give RF guided missiles what they wanted to look at without being limited by chaff,” says Brian Smith, senior principal systems engineer at BAE Systems. “This started the design of a program called POET, which stands for Primed Oscillator Expendable Transponder.”
POET – patented in 1975 by Martin Richmond of Sanders Associates (a BAE Systems’ legacy business) – was a decoy ejected from the plane that produced signals similar to those from the aircraft. As the decoy moved away from the plane, the signals confused the enemy radar, causing it to either follow the decoy or lose track of both altogether.
“Its electronic signature was bigger than the airplane that it was trying to protect,” says Smith. “So the incoming missile would latch on to POET instead of the aircraft.”
As threats evolved and technology advanced, enemies learned how to identify POET and other decoys of its kind – the decoys were free falling rather than “flying” as an airplane would, and enemy radars soon began to be able to detect the difference. While this eventually made POET ineffective, the technology set the stage for towed decoy devices – including our AN/ALE-55 fiber-optic towed decoy, which is still in use today.
A first of its kind
The AN/ALE-55 Fiber-Optic Towed Decoy was designed to be towed behind the host aircraft. Unlike traditional free-fall decoys, the towed decoy trails the aircraft and has a fiber optic link between the aircraft’s electronic warfare equipment and the decoy which is used to transmit jamming signals. These signals transmitted through the decoy serve to confuse and defeat threats thus protecting the host aircraft.
The fiber optic link to the decoy uses an electronic frequency converter (EFC) onboard the aircraft, to convert jamming signals from the aircraft’s electronic warfare system into fiber optic signals which are transmitted to the decoy over the tow line. The transmitted signals to the decoy, via a fiber optic cable, are then converted to jamming signals that are transmitted from the decoy to confuse and seduce missiles away from the host aircraft. The AN/ALE-55 Fiber Optic Towed Decoy allows aircraft pilots to execute their missions with state-of-the-art self-protection.
“This was the first ever fiber-optic towed decoy where we actually send electronic signals down to the decoy over a fiber optic link,” explains Allan McQuarrie, deputy vice president & general manager for Technology Solutions at BAE Systems. “The point of the decoy is that it provides superior self-protection to the aircrew. It is designed to confuse and protect host platforms against RF guided missile threats. If anything is fired at the aircraft. the missile would seek to fuse on the decoy versus the aircraft, if it even fused at all.”
The AN/ALE-55 program is still active today and recently celebrated its 2,000th delivery in September 2015.
Known as the Great-Grandfather to many countermeasure systems today, Hot Brick was initially developed in the Vietnam Era to defeat heat-seeking missiles.
During the Vietnam War, pilots greatly feared infrared missiles because they could accurately target and destroy helicopters or other low-flying aircraft by locking onto their heat signatures. The missiles were both portable and able to strike from anywhere without warning, making them a highly-lethal threat.
Aware of this, BAE Systems engineers developed Hot Brick – a technology that fooled infrared missiles by emitting a false heat signature.
“Pilots had no indication the missiles were coming. So we, as a country, had to develop countermeasure techniques to defeat those and the Hot Brick system was developed as one of those techniques,” explains Paul Squires, engineering manager at BAE Systems.
Testing of the system proved to be overwhelmingly successful; of the 18 missiles tested, all missed their targets. The test commander even ordered Hot Brick to be turned off when test missile 19 fired to make sure this wasn’t a fluke. Sure enough, test missile 19 hit right on target, proving Hot Brick’s ability to consistently confuse the heat-seeking missiles.
While Hot Brick itself was never used in the field, its incredible success in confusing missiles during the testing period spawned an entirely new approach to protecting aircraft. The concept eventually led to the further development of deterrence technologies by BAE Systems, including the AN/ALQ-144 Infrared Countermeasures system which is currently used to protect combat helicopters.