Blumberg, Germany — Saturday 13 November 1915

Georg was waiting at the Blumberg Market when David, Greg and Franz arrived and manoeuvred the lorry into position. After greetings, Georg said, "I'm surprised to see you here, Franz."

David took Georg aside, away from the ears of the gathering customers. "He's found what sounds like a perfect slab to cleave and send thousands of tons down onto the tracks. We'd like you to look at it and confirm his thoughts."

They continued to talk quietly as they watched Greg and Franz set up the stand. David told Georg about Herman's failure to meet them on Thursday. "Hans wasn't at the gasthaus yesterday afternoon, which means he had nothing to report."

"Could mean he's also in trouble."

"We'd thought of that, and decided that if two had run into something, there's no sense sending a third in. I decided to wait until this afternoon. If Hans doesn't appear, then we must begin thinking of the worst."

"Captured?"

David pursed his lips and nodded. "On to other things. What were your observations?"

"First, fifteen Pfennig seems still a good price." He pointed toward the lorry. "Let's go tell them, then take a walk."

Once they were away from the crowds, Georg began. "None of the viaducts is approachable. Far too heavily guarded. The same with the bridge over the Wutach River and the tunnel entrances and rock cuts. They know their vulnerable places. Hell, we quickly identified them." He smiled. "They've missed a couple, though."

"You've intrigued me. Continue."

"We're at the pass here, and it's a rather steady grade as they descend to the Wutach Valley bottom. There is huge momentum as the trains brake all the way down, using both steam and hand brakes. The trains have manned brake platforms every four or five cars to help keep the speed down.

"After I'd watched several trains, it occurred to me that a derailment could become a useful tool for us to take out a viaduct. With their guards concentrating on the vulnerable spots, there seems to be nobody watching the rest of the tracks. I've now identified two curves where a precisely located derailment would send a loaded train down the slopes and into a viaduct pier."

"I like that type of thinking. So you saw no guards, no patrols on the stretches between the viaducts and the tunnels?"

"None at all. I spent most of the daylight hours during the week searching and observing. It seems they don't think the intervening sections are vulnerable. They've laid safety tracks alongside the main rails to contain derailments, but they're useless if we blow them."

"It's like lining up a carom in billiards." David smiled and nodded. "Brilliant. Once the tracks are blown, the train will take a straight line, pushed onward by its inertia. Mass times speed. Huge energy."

"It will be moving across a slight slope, so gravity will have some sideways affect. We need to do a lot of calculation. Momentum, inertia and other things I know only a bit about."

"I love calculations like this. Likely Sergeant Perrier does also. He seems to revel in such things. We've all the elevations, plan views and sections in the archive, plus so many photographic prints and negatives. We should be able to set up diagrammatic models of suitable locations to help calculate forces and trajectories."

"That's what I thought. To me, it made no sense to measure the sites. That's already been precisely done by engineers."

"So you're finished here?"

"Except to confirm the results of my rough calculations. See if they make sense in reality. Setting up the charges should be quick and easy. We'll need a series of small directional blasts, all away from the cut so the curve remains unimpaired all the way to it."

"Without the continuity of rail, the curve will be straightened as cars roll over it." He looked at Georg and smiled. "I'm just making a mental note. There are a lot of forces involved. This seems an elegant solution. We'll need to get speed and weight information. I've a contact at the Embassy in Bern who is a railways expert. Skipworth will know how to access the technical data."

"I timed the cars going past the two curves of interest. It took between twenty-eight and thirty-two seconds for forty cars, and from pacing a train stopped to fill with water in Blumberg, I found the common boxcars to be twenty-seven feet long without brake platforms and twenty-eight and a half feet long with. My calculations show they're moving at close to thirty miles per hour in those two locations. They all slow as they approach the viaducts, but they speed up once they've passed them. Then slow again for the switchbacks."

"You were busy."

"Not much else to do except watch trains and pretend I was picking mushrooms." He laughed. "I actually found a goodly amount of them, but with the trains, I noted the time and numbers of cars in each train that passed during daylight the past six days. It's all in here." Georg patted his jacket pocket. "There was one down-bound and one up-bound every two or three hours, but I could see no pattern to their passing."

"Likely they depart as soon as they're loaded."

"It seems to be coordinated with the return trains, though. There's only a single track through here, so the unladen trains need to pull into the bypasses. My thinking is that traffic is controlled through each section from stations by telegraph and visual signals."

"We've a lot to analyse and calculate. I'm impressed by the information you've gathered." David looked toward the market. "Let's go help sell potatoes."