Air-to-Ground and Air-to-Air

CCXCI

The TR9D radio

Lightning struck in 1934 when Stuffy Dowding came up with the idea of installing radios in his fighter planes. At first the idea was dismissed out of hand. Radio components were too heavy, too bulky, and above all too fragile to take to the air in fighter planes. How could anyone jam a big radio box into the “I-put-it-on-I-don’t-sit-in-it” confines of a fighter cockpit?

Stuffy pointed out to the naysayers that all their objections had to do with the limitations of the available technology, but not the concept itself. He argued that if a (relatively) compact and (relatively) lightweight radio could be developed, the RAF would be in the proverbial catbird’s seat when it came to air combat. 

Radios were indispensable in Dowding’s overall view of British air defence. Unlike pilots in World War I, who could rely on hand signals as directions from their compatriots when they were in combat formations, pilots in the coming war would need to exchange fast, complete, and above all, accurate information with HQ and with other pilots.  

Stuffy’s answer was the TR9D radio. As its name implied, it could transmit and receive. It was powered by a small windmill on the exterior of the aircraft.  The TR9D was uncomplicated, easy to repair, and easy to replace. In terms of its dimensions it was not much bigger than a FedEx envelope cubed. It had simple operating instructions and only a single channel.  

The antenna position on the Hurricane (top) and the Spitfire (bottom)

 

 

The antenna stretched back from a housing just aft of the cockpit to the top of the rear vertical stabilizer.  It worked in the AM band. As long as everyone in the squadron was on the same frequency, they could hear one another and ground control. Under noncombat conditions the radio chatter was tolerable, though during combat the box did tend to get rather squawky. 

In 1937, the first planes to get the TR9D were the Gloster Gladiators, the all-metal biplanes that were about to become so magnificently obsolescent. Then they were installed on the Hurricanes. The Spitfires installations came last, but just in time to do their part. 

The ability of pilots to receive flight information from the ground and to coordinate attacks in real time was central to the RAF's victory in the Battle of Britain. Never had so many owed so much to so few vacuum tubes.

Schematics of the TR9D