Bridging

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I'm coming back to this graphic

once again. It shows (with the larger green circle) the approximate rumoured range of Iskander precision-guided ballistic missiles launched from the Russian Kaliningrad Oblast (rumoured ~499 km).

A closer look at the geography shows that two of three major rivers that are between Western European allies' land forces and Lithuania (Vistula and Oder, not the more Western Elbe) are in range. The Oder is just barely in its rumoured range.

9M723 Iskander (SS-26 Stone) has enough claimed accuracy (CEP of few metres) to be capable of hitting a bridge WHERE you tell it to hit, not just hitting the bridge at all. The cruise missile that can be launched from the same system has most likely the same range, and as a cruise missile it could approach a bridge horizontally, to penetrate and blow up from the inside the abutment.*

Successful strikes against the railroad bridges would no doubt disrupt rail traffic for weeks. Successful strikes against the road bridges on the other hand could be compensated with military engineers, maybe even within a day. More about that later. First, I'd also like to add that there are railroad and road connections between Slovakia and Poland that circumvent the Oder, but their capacity is lesser, using them would be a great detour for Western forces, the terrain is mountainous and might be troublesome for some vehicles (I suppose tank transporters would have trouble, at least in icy conditions).

So how could military engineers (Pioniere) compensate for destroyed bridges? Grid-style steel bridges are rather unlikely to be erected within days, but pontoon bridges can be built real quick. There are certain limitations, though.

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600 German and British engineers exercised such pontoon bridge-building this summer on the Vistula as part of the Anakonda 2016 exercise, with both armies using M3 Amphibian rig vehicles and (un)folding pontoons to quickly create a 350 m wide pontoon bridge under near-ideal conditions.

Nominally, they would need 8 vehicles per 100 m bridging, but they needed 30 for 350 m this time, slightly more per metre.

more imagery (and German text) on M3 Amphibie

more on Think Defence about pontoon bridge history and M3 Amphibian rigs

The pontoon bridge was created (after due preparations) within 34 minutes. An engineer tank tested the bridge's stability, then it was cleared with a capacity of 250 vehicles per hour. That's one fourth of a brigade per hour, minimum four hours per brigade (there need to be spacings between units to avoid bunching up, since bunching up attracts fires and provokes traffic jams).

Now about the near-ideal conditions:

- very shallow water

- slow stream (2 m/s) that required no anchoring of the amphibian vehicles

- plenty time for preparation

- units knew in advance of the exercise and were able to ensure high vehicle and personnel readiness 

- no hostile actions

- no river flood (really big ones happened in 2010 along the Oder)

- river shipping was stopped in time

Germany has 30 M3 Amphibian rigs in active service (and apparently some more in storage), the UK 38. Others were exported past NATO's borders, the production total was 110 apparently.

With normal readiness and normal river width in mind and with the French inventory of similar amphibious bridging vehicles in mind one could expect 3-6 such pontoon bridges to be created. I have no idea whatsoever about the Polish inventory and capability in this regard; I can only guess that they would have participated in the exercise if they had anything similar. Their PTS vehicles are nowhere close in capability.

Two or three routes with 4-6 such pontoon bridges might be established across Oder and Vistula approx. within 24 hrs after strikes on the normal bridges, but maybe it would take 48 hours - this depends on the readiness of the units.

The capacity of two such routes with 250 vehicles/hour might suffice for alliance purposes, but it sure wouldn't be luxurious. Even with every vehicle a lorry with an average of 10 tons cargo, this would only be 120,000 tons throughput per day on two routes maximum. Realistically, it would rather be close to 50,000 tons per day taking into account that not only supplies, but also reinforcements would cross those bridges. 50,000 tons supplanted by what crosses the mountain passes of Slovakia - enough for approx. 12 divisional equivalents, or ~36 brigades. That's plenty supply capacity compared to what could be in (arrive at) the region within a week or two, but not much if we consider the supply needs of non-divisional forces, the possibility of damage by hostile action, or the quantities of forces that we'd want to have by the NATO doctrine of "counter-concentration" in the event of crisis.
And of course this capacity is one-way only; to maintain this throughput in one direction no vehicle would be allowed to return.

One might arrive at the conclusion that reactivating whatever M3 Amphibian vehicles are in storage and adding a few more simple steel (un)folding pontoon elements to the inventory may easily be worth the expenses in terms of deterrence and defence. The current inventories look to be close to the minimum requirements, without any robust reserve capacity.
We should also think about how to defend such pontoon bridges against air attack.

Furthermore, the battalions (German, UK and French) that can build such pontoon bridges should be held at highest readiness, second to no other land forces elements.

S O

defence_and_freedom@gmx.de

*: I suspect this is what the "bunker penetration with cruise missiles" craze of the 1990's and 2000's was in part about.  Bunkers alone could not explain the quantity of such missiles purchased, even if we count hardened aircraft shelters (which would not require that very much dedicated ammunitions). Germany alone purchased 600 Taurus missiles!

edit October 2016: The French system

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