During the first world war both sides engaged in tunnel warfare, the primary purpose of which (as far as I can tell) was to place large amounts of explosives under enemy lines and then detonate them immediately prior to ground attack.

Was there ever any attempt to use a tunnel to bypass the front line to get soldiers directly behind enemy lines?

My understanding is that in a conventional attack, by the time any of the attacking soldiers reached the enemy front line, they were likely to be wounded, shell shocked, possibly alone, separated from his unit, low on ammunition and likely to be seriously demoralised! and that was before they'd actually got to engage the enemy themselves!

With so much tunneling going on (Wikipedia quotes 2km of tunnel for every 1km of front line) couldn't a tunnel be dug that could surface at or behind the enemy front line and allow groups of fresh, uninjured, well rested soldiers still in battle formation to quickly deploy having bypassed the majority of the barbed wire, trenches and machine guns?

Update - Here's the wiki item on tunnel warfare. For clarification - I'm not suggesting a major attack exclusively via a tunnel, I'm assuming it would play a supporting role in more conventional attack. A few hundred soldiers appearing behind enemy lines 10 minutes before you go the top has give you some advantage doesn't it?

Also please note, the main thread of this question is "did it happen?" so far most of the comments, although interesting, are just listing reasons why it probably didn't.


UPDATE following further research. Apparently there were too main types of tunnels, 'fighting tunnels' small, narrow tunnels dug silently under enemy lines for the planting of mines, and 'subways' larger, wider and longer tunnels used to get troops discretely and safely up to the front line. The subways could be a mile or two long and would be used to bring large number of troops to the front line trench immediately prior to an attack. I guess that these 'subway' tunnels were only really practical behind the lines because they could be dug without having to worry about being disturbed, and regular ventilation shafts could be sunk without giving the position away.

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    One problem would be getting enough soldiers through the tunnel quickly enough to launch a worthwhile attack. If they were spotted before a sufficient number of troops got through, it would have been a massacre. – Lars Bosteen Oct 17 at 12:49
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    @Lars Bosteen - You are right, but a conventional head-on attack would involve a massacre anyway - could easily loose 50% of the first wave. – Hemel Oct 17 at 13:05
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    @Hemel That's still with people supporting each other, as well as artillery and (limited) air support. Digging behind enemy lines completely removes friendly artillery, any support soldiers can provide each other, recovery of wounded soldiers... actions behind enemy lines are always extremely tricky, and having to reach those lines through narrow tunnels makes it even worse. It's like trying to force an engagement with a superior force in broad daylight while crossing a river. The tactics in WWI had their sore points, but this would be even worse. – Luaan Oct 18 at 10:36
  • @Hemel And keep in mind that the real reason the frontal attacks didn't work wasn't that they could get to the enemy trenches and occupy them - it was that they couldn't ever hold them against the inevitable enemy counter attack. There were multiple lines of trenches, and reserve troops behind the lines that reinforced any location that needed help. In the frontal attack, this forced the (tired and wounded) attackers to retreat - in you scenario, they would be caught between two well-rested lines of enemies with no possibility of retreat. – Luaan Oct 18 at 10:41
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    @Hemel One of the thing that made those frontal attacks so deadly was the rapid and sustained fire rate of the machine gun. Now imagine that instead of the machine gun having to cover a whole line of enemy attacker, it would just need to aim at the exit out of a tunnel. Again, you've made the original problem worse, not better. And don't think they couldn't find the exit tunnel fast enough to prevent the attackers from establishing a beachhead - again, the frontal attacks routinely succeeded with that part anyway. – Luaan Oct 18 at 10:47
up vote 34 down vote accepted

One of the main problems with any mine, military or resource-extraction, is ventilation. It was clearly not possible to dig ventilation shafts in No-Man's-Land, so all the air for the tunnel occupants had to be provided by (man-powered) fans at the entrance; not easy, even for a party of engineers bringing up explosives. The idea of providing oxygen for several hundred men in a tunnel long enough to bypass both front lines would make a miner either laugh or weep, even before he considered the other problems.

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    Ventilation is a good point...even with just the handful of men they had in tunnels they did dig it was an issue, carbon monoxide levels were a problem due to all the gun and artillery fire and while rebreather equipment existed it was in insanely short supply. – motosubatsu Oct 17 at 20:10
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    Image if they were to succeed (however unlikely).... Then you now have some 100s men isolated between enemy lines which need to be supplied through a tunnel which might collapse at any time... – User999999 Oct 18 at 10:00
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    There's also the problem of not digging the tunnel far enough - it would have to stretch beyond the support and reserve trenches (200 - 500 yards + no mans land) and would still be in front of the artillery among the supply lines which would no doubt be very busy. – Darren Bartrup-Cook Oct 18 at 15:54
  • This seemed surprising to me, and a little Googling makes me confident that it's wildly wrong. There's apparently enough oxygen to survive for hours in a sealed coffin, and it would only take a few minutes for a line of hundreds of men to pass by any given coffin-sized slice of tunnel. Even if you had no ventilation once the men started moving through the tunnel, and even granting that a man moving through a tunnel might use several times more oxygen than one lying in a coffin, just the starting oxygen available in the tunnel would be far more than needed to get hundreds of men through. – Mark Amery Oct 19 at 11:53
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    @MarkAmery: you may want to add to your scenario a bit of ventilation logistics to create the tunnel in the first place... – Olivier Dulac Oct 22 at 9:24

While I like your thinking there are a few issues with such a plan:

  • Emerging behind enemy lines means there may well have been other enemy troops (just as fresh) in the general area.

  • With WWI technology it would be extremely difficult to reliably pick (and hit) a suitable exit point. Tunneling to the lines was comparatively much easier in terms of judging the distances etc. Also if you were slightly off the explosions still stand a decent chance of doing at least some damage to the enemy forces, and the distraction element (thus allowing your forces to close the distance overland) would still be largely intact.

  • Digging a tunnel large enough for moving substantial numbers of men in a reasonable timeframe would be difficult - especially with WWI technology and battlefield conditions (digging a tunnel to place a single mine could take nearly a year and they would be much, much smaller than one capable of moving troops)

  • If you did manage to dig a wide enough tunnel to move enough men to make it worthwhile the tunnel exit point would need to be wide as well - otherwise they are just coming out single file and one enemy soldier with a decent firing-rate rifle/gun and suitable piles of ammo could hold such an exit for as long as they want to really.

  • In order to dig a tunnel exit sufficiently far back that it wouldn't be noticed (and either wide enough to allow troops out more than one at a time or in a quiet enough location to give you room to form up before attacking from behind) the accuracy in digging and positioning simply wasn't there in that era - not into territory controlled by the enemy certainly.

  • Also if you built a wide enough tunnel (as above) you'd have the problem of keeping it stable - wide tunnels need matching amounts of structural re-enforcement to keep them from caving in under their own weight (technology would have been one of the limiting factors again as would time). And that's even before you take into account that the ground above will likely be receiving hits from mortar shells, tanks and other vehicles rolling across them and so on. Losing a substantial number of troops to cave ins would have been very probable, especially when you consider that digging such a large tunnel would have been difficult to keep covert, so if the enemy knew one was being dug it would be trivial to collapse it.

Conventional "over the top" charges weren't a good solution either (as you correctly point out) but considering the above it's difficult to see tunneling being any better - and quite possibly worse. Much of the "advantage" of such a plan relies on the enemy not knowing you were coming - you may be able to pull it off once or twice but after that it would be easy enough to prepare for it and there goes the element of surprise, and once the Germans had used tunneling to place a mine against allied forces (to great success) both sides were not only tunneling themselves but were actively watching and listening for enemy tunneling operations.

Update following the OP's own

To more directly answer the clarified question I'm not aware of any recorded instances where tunnels were used to directly place troops behind enemy lines in WWI where the troops themselves were used for the offensive action themselves, presumably because (when you consider the issues described above) it was nearly logistically impossible and in any case would struggle to be more effective than a mine/mines and far more dangerous.

The sort of "advantage" you describe (which I still think is highly unrealistic in the scenario; moving "a few hundred men" and their associated equipment through a WWI-era tunnel, undetected and in fighting shape when they arrive is pure fantasy IMO) would be negligible, when you look at the sheer scale of the troop numbers involved you can see why - on the 1st day of the Somme the British alone brought 13 divisions and a division was approximately 16,000-18,00 men so that's 208,000-234,000 men - a "few hundred men" wouldn't even move the needle on a battle of that scale.

And when you compare the offensive potential of a few hundred (or even a few thousand) infantry troops compared to the destruction even one of the mines could cause, not only in terms of enemy troops killed or incapacitated but the destruction to infrastructure, artillery and machine gun placements, and equipment it's not hard to see why no-one tried the idea of using them to deploy troops directly.

It really is no-contest: The Lochnagar mine alone obliterated approx 300 to 400 feet of German fortifications including nine dugouts!

Offensive mining was by no means a perfect strategy (trying to traverse a 300ft crater with infantry troops created something of a killing ground and combined with some sub-par infantry tactics didn't exactly help matters) but tunnel-deployment would likely have been a 99% certain death sentence for the men in question if the enemy soldiers didn't kill you your own side might - this was the era of large scale shelling, and wouldn't have achieved anything for it.

All the troop-on-troop conflict in WWI tunnels that I'm aware of took place in the tunnels themselves either by accident (tunneling into an opposing tunnel by mistake was quite common) or deliberately to counter a detected tunnel (at least in the early days of tunnel warfare the German tunneling techniques were much louder than the virtually silent "claykicking" employed by the British forces)

The closest I can think of to the sort of tactic you propose was the Chi-Chi used by the VietCong during the Vietnam war and it was reasonably effective - but that's a whole different tactical situation from the relatively static trench warfare scenario seen in WWI.

  • All valid points. The technique I had been thinking of was to build a single-soldier-wide tunnel from your side to the enemy front line, fanning out into a set of staging tunnels with one exit for each group of soldiers. The soldiers could be moved through to the staging tunnels before a final break out would be made using a pneumatic ram - something like was used to raise the Livens flame projector. – Hemel Oct 17 at 13:38
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    "Wide enough": you need not only soldiers, but equipment, supplies, artillery. Then large tunnels were routinely detected… For a small incursion: maybe good? For an offensive, not viable at all. Could you add some references for WWI tunnel warfare? – LangLangC Oct 17 at 13:52
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    You could add: if you have rear and frontal attacks against an entrenched enemy, you risk causing more casualties by friendly fire than you cause to the enemy. – Peter Taylor Oct 17 at 15:17
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    @Hemel Not viable at all - both sides were tunneling, constantly and intensively. As for the pneumatic ram idea - if you were to dig a tunnel spacious enough to actually operate one it would have to be deep enough underground that it would be useless. In most of the tunnels dug in WWI it was too cramped to operate a rifle let alone a pneumatic ram. Not to mention of course you'd be doing so in near total darkness (candlelight for the most part), almost certainly partially flooded and of course there was always the joy of natural gas pockets to contend with... – motosubatsu Oct 17 at 16:29
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    @Hemel each human requires a cubic yard. To put a significant force of 10,000 troops underground, you'd need oxygen (!) and 10,000 cubic yards (and the soldiers are packed in tight). If your tunnels are 1 yard in diameter, that is 5 miles of tunnels. A long tunnel is 1000 yards long. And defences where in depth, so where you come us is probably aimed at by artillery and machine gun fire and cut off from resupply. – Yakk Oct 17 at 16:54

While the above answers are quite valid, here's something else to think about: It's highly likely that the enemy would pick up on a tunnel dug for such a purpose, and move to defeat it, as counter tunneling efforts included listening systems to detect the construction and use of tunneling. Having many men stationed in the tunnel prior to the attack would be relatively easy to detect by that method, and so betray the presence of the tunnel.

There are 3 problems to the idea.

  1. The defense systems of WWI (particularly those on the Western Front) were often multiple miles deep. To tunnel behind the enemy line would easily require a tunnel a few miles long.

  2. Given the limited flow of manpower over such a small pipe, it would be a fairly simple exercise for the defenders to contain the troops coming out of the tunnel.

  3. the combatants had fairly sophisticated anti-tunneling capabilities, as tunneling was not a new idea.

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