Originally Posted by
Spunky Monkey
To use shaped charges as several people have suggested, they need to be in direct contact with the metal you are are trying to cut. Placing a charge even a couple of inches away will not cut a train rail.
Placing a boat load of explosives under the bridge even if it is just 20 feet between boat and span will loose a great deal of its shock wave effect (Which is what you use to destroy a fixed structure).
A lorry load of explosives would be the same issue, the bast would likely result in a crater roughly the size of the vehicle and would not be likely to create enough of a shock wave that brings down several non adjacent spans.
This could be an inside Rusk escalation with charges attached to the joints of one of the bridge junctions, including an accelerant / vaporiser.
The second option is a very large air delivery munition, by choosing a lower span, there is more opportunity for secondary shockwave reflecting back off the sea. I wonder if the lower height of the piers means. less flex in the sea creating a more rigid structure than targeting a higher level pier.
Is a long time since I did dems but we always used to look a channelling the shockwave.
Shaped charges most assuredly must NOT be in direct contact with the target. They
require a standoff distance related to a multiple of the width of the charge as per the individual design. In the case of a custom-made charge built into a boat it could be a vary wide device ndeed - say a metre. A 5 times standoff distance would be at peak effitiveness at 5m, about the height of the bridge I'd guess, and such a charge laid along a boat is in the perfect alignment to sever a structure like a bridge from edge to edge.
In any case a sufficiently large in a boat under a bridge is simply going to lift it up in the air and let it drop or with enough brisance simply shatter the concrete. The blast pressure will be 'loosed' (sic) in all directions, but the water will tend to reflect much of it upwards where you want it.That'd do the job too.
If you imagine a ton or more of explosive is defeated by a 20ft airgap or only leaves a 'crater' the size of a vehicle you are way, way off the mark.
The lack of obvious scarring suggests a blast from below which had the added effect of projecting debris upwards to puncture the tank-cars.
No way was this air delivered or the defences would have lit up like Novemner 5th.