Jeremy handed out wooden blocks cut from a 2x4 and some 550 cord. The blocks had holes drilled to represent an insertion point for either detcord or a blasting cap. The winter classes filled up fast with volunteers from the refugee camps in the province. Jeremy hadn't been a combat engineer since Vietnam, but he transitioned that career into a civil engineering degree and a successful career working for the Department of Transportation overseeing construction contracts.
He hadn't cared one way or another about who was in charge, new boss same as the old boss, until his daughter got swept up in a protest raid at college and raped in the holding pens the police had set up to handle the overflow of "criminals." Sarah had gotten knocked up and while they loved their new grandson just as much as any of the rest, Jeremy couldn't forgive the cops who looked the other way when one of their own decided to rape a prisoner. If they would close ranks to protect one of their own, then guilt by one was guilt by all according to Jeremy.
Anyways, Jeremy found out how vengeful the thugs could be, blow up one tiny police motorpool and your name is mud forever. Jeremy made it across the border less than a day ahead of his arrest warrant being signed and being added to the "most wanted" list. But he had made it, and his family too. Within days of arrival Jeremy tried to find a way to give back to the people who took him in. When Jeremy had told the camp commander that he could train on
demolitions with just scrap wood, 550 cord, modeling clay, and tape, he
was met with a chuckle of disbelief. But the commander figured it couldn't hurt, and the first class was such a success that regional commanders were sending up experienced fighters to get prepped for bigger missions.
"British junction to an I Beam cutting charge, go!" Jeremy started his stop watch as the students began taping blocks of wood to the I Beam. The smart sapper got a recon of his objective so he could make the charges needed ahead of time, instead of futzing around with explosives on the objective.
"All right, 55 seconds, not bad." Jeremy said as he inspected the taped 550 cord to ensure that it was actually equal length, that the British junction (the point where the cords come together on a common ignition source) was taped tightly together, that none of the 550 cord was laying across any. Detcord explodes so fast that you have to be careful to not let it cut itself and stop the detonation. Jeremy found one "block" that had a single strand of 550 cord in it as a detonator, "Ok folks, see this? Remember two is one and one is none when it comes to priming explosives. But other than that, excellent work."
"Ok class, these blocks represent C4, can anyone tell me if this charge would have been successful using blocks of TNT?" Jeremy smiled.
"Yes Sir" A red bearded man spoke, "The amount of C4 we used was twice as much as called for for the I beam, and the Relative Effectiveness Factor for C4 against TNT is 1.3. Since the REF is between 1 and 2, and we used twice as much to start with we ensure that it would work, even using TNT. Assuming that the blocks are a measurement of weight, and not a measurement of volume."
"Good job Rob." Jeremy smiled. "Did everyone follow?" Heads nodded and shook with almost an equal mix in the group. "Ok, back to theory one more time." There were some groans when Jeremy went into "lecturing engineer" mode.
"Explosions are very simple, they are a matter of shape, amount, and composition. Explosives explode at different velocities and different energies. Low explosives detonate at a speed less than the speed of sound, high explosives detonate faster. To get the same effect from different explosives, you need to use different amounts, and we compare them with a "Relative Effectiveness Factor" as compared to good old TNT." Jeremy saw heads nodding.
"Rob knew that we used twice as much C4 as we needed to, and he knew that C4 doesn't have an REF lower than 1, so using the same mass of TNT would successfully cut the I Beam." Jeremy smiled. "Look, I'll teach you how to do the math a couple more times before the test, but in real life you'll just consult the reference book depending on the composition and thickness of whatever you are trying to destroy. But bottom line, if you calculate for C4 but all you have is TNT you need to increase your charge by 30% to get the same effect as using C4."
"Ok, anyone want to tackle an abatis for extra credit?" Jeremy smiled as several people groaned. "All right, independent study for the next two hours, break out into small groups. Group A, satchel charges and tactics appropriate for them. Group B, cratering charges and tactics appropriate. Group C, entry charges through brick, masonry, and concrete. Group C, steel cutting charges for a reinforce door and minimum safe distances."
So far graduates of Jeremy's impromptu engineer academy had destroyed several million dollars worth of war machinery by dropping a train pulling equipment into a canyon a la "Two Mules for Sister Sarah" and sank several cargo ships transitioning the straights under cover of darkness, at least until the CG stepped up escort patrols. Jeremy sipped his dark coffee and answered questions, usually about math, from the study groups.
Jeremy taught at Freedom Camp 7 for two years before he died of a heart attack, possibly modern medical care could have extended his life but when his family read his "just in case" letter they knew that he died a happy man. He was buried deep in the forest in the spring rain, right next to a boulder deposited by a retreating glacier eons ago. To this day Engineers make the thirty mile hike to leave a regimental crest or piece of 550 cord tied into a Uli knot at Jeremy's boulder.