Other Earths (collection)

We passed the first shape. Because the road snaked a bit, I was able to see that the front of the object didn’t have any doors or windows either, and no sign of gun slits. The main part was a big concrete bowl with a thick rim, tilted almost onto its side so that it faced out to sea like a great curved ear. The bowl was easily fifty or sixty feet across, and its lower rim was about thirty feet off the ground. It was attached—or cast as part of—a heavy supporting wall with sloping sides made of the same dreary gray concrete. A windowless hut was positioned under the rim of the bowl, and rising from the roof of this hut was a metal tower that ended in a pole, sticking up so that it was in front of the middle part of the bowl.

“They’ve built them big now,” Ralph said. “They were only about half the size when I was here last.”

“I’ve no idea what this is all about, sir.”

“Really, Wally?”

“Not a clue, sir.”

The ambulance slowed a little, and we passed a concrete plinth on which was mounted a curious object, resembling a flattened searchlight on a cradle that could be aimed in various directions. Two men were sitting on chairs attached to either side of the moving part of the cradle. In addition to their gas masks they were wearing heavy black headphones. The men were gripping levers and steering wheels, and as we passed the cradle, it tilted and rotated, making me think of a sleepy dog suddenly waking up to follow a wasp. A third man was standing next to them holding a portable telephone to his ear.

“The name of the game’s acoustic location,” Ralph said, before looking at me expectantly. “I expect it’s all as clear as crystal now?”

“Not really, sir. But you said ‘acoustic’—I presume this has something to do with sound?”

“Very good. This is one of the main stations on the south coast. Those chaps we just passed are listening to the sky; that thing they’re sitting on can pick up sounds from tens of miles away.”

I thought about that for a moment. “Won’t they have been deafened by us driving past?”

“No more than you’d be blinded by the sun if you were looking in the opposite direction. The receiver only amplifies the sounds coming into it along the direction it’s pointed—nothing else matters. Those chaps steer it around until they pick up the drone of an incoming airplane, and then they nod it back and forth and side to side until they know they’ve got the strongest possible signal. Then a third chap reads off the elevation and directional angle and telephones that information straight to the coastal defense coordinator, who can then telephone instructions to the big guns or the Flying Corps.”

“When we were told to point our guns, sir, I always assumed it was down to spotters.”

“Which was undoubtedly what they wanted you think. Not that the Huns didn’t have their own stations, but we always reckoned our coordinating system was superior. On a clear day, when the airplanes are within visual range, a spotter will always do a better job than the sound men—it’s all a question of wavelengths and the problem of building sound mirrors much bigger than the ones we already have. But when it’s dark, or the weather’s closed in like this, and the aircraft are a long way out, the fix provided by the sound stations gives us several minutes of advance warning.”

The second concrete shape was now to our right. I noticed that the rim of the dish was missing a big chunk and some concrete rubble was lying on the ground under it—it was as if someone had taken a nibble from a biscuit. A man with white gloves and a gas mask was standing by the hut directing us to continue driving.

“Looks like they took a direct hit,” I said. “What do you suppose it was?”

Ralph steered for the third shape. “Flying wing or long-range shells. Doesn’t make much difference now—the one’s as bad as the other.”

“Are the concrete things the same as the one the men were steering?”

“Same general idea, just scaled up. The men call them sound mirrors, which is what they are, really—giant mirrors for collecting all that sound and concentrating it on a tiny spot just in front of the dish.”

“I don’t see how you can steer one of those, sir, let alone nod it back and forth.”

“You can’t, obviously. But you can move the pickup tube a little, which has a similar effect. The three of them are pointed in slightly different directions, to cover likely angles of approach. On a good day they’ll pick up the bombers when they’re still grouping over France.”