"How many bombs to destroy a bridge?" Topic

Am working on some damage charts for BTH2. Have the ship stuff done and actually finished up rockets today. Having problems on some of the land damage.
How many hits on a "typical" 2 lane steel/concrete bridge would it take by 500lb bombs to destroy it? 250lb bombs? I am guess a 1 lane bridge would be abotu 66% as strong.
Answers or leads would be appreciated. Not going for perfect accuracy but an approximation.

Thanks

Joe

Totally depends on the construction method, how it is 'anchored', where the bombs actually hit, etc. Even the types of bombs would make a difference.

I'd just run with a wild ass gut guess. X factor to hit the bridge, then Y factor to actually a) damage it, b) knock it down for a short period of time (X time) and c) it is totaled. You cannot go wrong from that.

Dan

We do this with 2d6 to hit: first die picks the d6 direction from the "aim point", second d6 is inches "off" in that direction. THEN, there is the full-damage burst center, with a half-damage outer ring. Depends on the scale of the game. Rocky Russo could chime in here with blast radii; I don't know off-hand what they were for the various weights of bomb. We do damage with numbers of d6s, and the total comes off the points of strength/resistance of the target. The range of d6s to roll for full damage might be: 3d6 for 100# bombs; 5d6 for 250#; maybe double the roll for 500#….

Also a bridge might still stand but be impassable to vehicals but passable to troops.

Hmmmm, I'm guessing a 500 lb. bomb, with a direct hit, centered on the target should take it out.

It would definitely be impassable to vehicles, but infantry might still be able to use the sides, if still standing.

For others, and near misses, it runs the range from cosmetic damage, to heavy damage, depending upon the location.

Getting a direct hit is probably a 1 in 1,000 shot, for a single bomb. 1 in 500 if you drop two bombs at the same time, in a low-level pass.

This assumes that the bridge is a short, two-laned bridge, as mentioned above.

Hitting it would be the super-hard part. Also, if the bridge is flimsy a bomb might pass right through without detonating right away.

Depends on what you mean by "destroy". If you are talking about having the bridge fall in the water, then it is unlikely a single hit will cause a collapse.

If you are talking about reducing the structural integrity such that heavy vehicles such as tanks can't pass then it is highly variable – it would depend on the original weight limit of the bridge, how redundant the spans are and how well maintained the bridge is.

As evidenced in the US in recent years, merely driving traffic across a bridge can cause it to collapse.

You are probably better off just abstracting the to hit number to something low within game range (i.e. double 6's on 2d6) to get a damage result with a second roll of 2d6 (double 6's) to determine a "critical" bridge kill or heavy damage. Blast from bombs is unlikely to do much damage against stone or heavy steel bridges and there is little frag effect from HE that would matter to a bridge. So anything but a critical results in "light damage".

-Binhan

1, but it has to be the right bomb in the right place….

I spoke with a Danish pilot 10 years ago. He was a flight leader in the RAF who flew Tempest MKII aircraft during WWII. He told me he took out a large bridge with two 500 pounders in late 1944 -- he said he cut the bridge in half. He said he approached the bridge at water level and at the last moment climbed, then released the bombs. When looked back, the bridge had collapsed.

My father flew in the Fleet Air Arm and has told me similar – a direct hit with a 500lb bomb will do an awful lot of damage even against shipping.

"How many bombs to destroy a bridge?"

One, in the right place.
How you work out where the right place is, is quite another matter, and given the inaccuracy of free fall bombing in WW2 any hit on the right place (even if you knew where it was) would be purely a matter of blind luck.

Let's find out 1….2….3 BOOM How many bombs does it take to blow up a bridge? The world may never know.

A Lot more than you think for example using the tables in general notes on the use of artillery 1917 the amount of ammunition required for destroying a railway bridge is given as between 100 and 200 rounds depending on calibre of round fired (the table gives up to 9.5in shells) if firing in enfilade and between 400 and 800 rounds for frontal fire

the problem is not how many hits it takes to destroy a bridge but how many misses it takes to hit it

I have n extremely handy WW2-era handbook on weapon efefcts against structures. Drop me a line offlist and I'll see what I can do, if that sounds useful.

"the amount of ammunition required for destroying a railway bridge is given as between 100 and 200 rounds depending on calibre of round fired "

Artillery rounds are usually not as big as bombs.

GreyOne wrote:

I spoke with a Danish pilot 10 years ago. He was a flight leader in the RAF who flew Tempest MKII aircraft during WWII. He told me he took out a large bridge with two 500 pounders in late 1944 -- he said he cut the bridge in half. He said he approached the bridge at water level and at the last moment climbed, then released the bombs. When looked back, the bridge had collapsed.

Your man is obviously doing it the right way. Bridges are designed to take considerable downward stresses without collapsing. So, it was discovered that the best way to knock over a traditional stone arch bridge is to attack it from underneath. Skip a bomb from the river, or make a climbing delivery, and you should pop the keystone nicely and leave bits of bridge all over the place. Hairy flying required, of course, but, hey -- fighter pilots.

However, Mr. Picky would like to point out that, whatever else he might have been flying in combat in 1944, it certainly was not a Tempest Mk II.

All the best,

John.

"However, Mr. Picky would like to point out that, whatever else he might have been flying in combat in 1944, it certainly was not a Tempest Mk II."

He flew many aircraft during the war, but mostly low level flying and attacking ground targets. His favorite aircraft was the Tempest MKII, but he also flew everything that had a single engine in 1944, including Spitfires (I suspect he flew mostly RAF aircraft). I spoke with him on his death bed -- he died three weeks later. I think his memory was merging images and facts together at this point in his life. However, he was very interesting to talk with.

The reason he told me about destroying the bridge was because he was only about 23 years old at the time and was leading a flight of aircraft to destroy the bridge. He flew in low, along the water level. He said you could also avoid most anti-aircraft this way. He said he never forgot the mission because he was told the bridge would be crammed with German vehicles and personnel. He was lining up the bridge and the at the last minute noticed that the bridge was crammed with military vehicles and civilians. He was not told there would be civilians. He figured he killed between 300 and 500 people that day and it bothered him, quite literally, to his grave. He never told anyone about the incident, except he told me. His family never knew.

Mike i know aircraft bombs are on the whole bigger tham artillery rounds but the point is it takes a lot of misses to get a critical hit

and a 9.5in shell weighs 380lbs and a 12in shell 750lbs well within the range given by Joe in the first post so the data has merit

Thank you for all the feedback. Let me clarify my original post. I am modifying the damage charts for BTH2 not the "to hit" sequence. Thus my question really is how many bombs that have hit would it take to destroy a bridge? "

I want to abstract where the bomb hits and to a certain extent the construction of the bridge to keep it relatively simple. If my flight of Tempsets is bombing a bridge and they hit it, on average how many bombs would it take to: render it impassible except to humans? render it impassible except for small animals? drop it into the water?
I plan to use a die chart to account for the lucky hit or glancing blow. My guess (I am a surgeon not an engineer) would have been 2 500lbers 4 250lbers but those are guesses.
David Manley I do not have your email address but you can reach me at joseph dot legan @ langley.af.mil

Thanks again for your help. The data for ships was much easier to come by.

Joe

Joe,
For reference, a Ju-87 on really good day under really good conditions can drop a 1100 lbs bomb within a 100 radius circle. Assume most medium bridges are 20-30 feet wide and a certain length, the % area of overlap between the rectangle of the bridge (20 ft wide) and the circle of accuracy (100 ft radius)is about 12.7%.
So if you go with the idea that only a direct hit is going to matter, under optimal conditions it will take 8-9 bombs to hit and destroy the bridge.

-Binhan

-Binhan

Binhan,
Are you saying it will take 8-9 bombs dropped for 1 to hit the bridge thus destroying it? Or are you saying it will take 8-9 bombs hitting the bridge to destroy it? I would think 1 1,000lb bomb would destroy a medium bridge or at least blow a hole clean through it.
Thanks

Joe

Joe,
8-9 bombs to get one to hit (on average). Depending on your damage model, one direct hit with a 500 lbs bomb could drop the bridge, or reduce it by one level of usefulness i.e. from being able to carry tanks to carrying trucks to pedestrian, etc.

-Binhan

Binhan,
That is my question. On average, how many hits by 500lb bombs would it take to destroy a bridge? I am trying to come with the damage model. The "to hit" model is done.

Thanks again

Joe

Speer overlaid bomb crater patterns on the Rhine bridges, decided that they would be easy to take out, and feared that the Allies would destroy them and then invade on the Baltic coast, having trapped the German armies on the western side of the river.

So he put in place repair materials near each bridge.

He didn't know about Valkyrie at the time; that was the plan to quickly organize all troops in Germany on leave & sick & rear-guard.

From a pure SWAG: one hit with a 250lb bomb will drop a bridge one level of usefulness (tanks to trucks). 500lbs (whether 1x500lb or 2x250lb) will drop the bridge two levels (tanks to personnel), and any more boom than that drops the bridge entirely.

Lion,
Thanks for the SWAG. I was thinking as my own SWAG that a 250lb would do one step about 80% of the time.
500lb would do one step 30%, two steps 60% and destroy 10%
1000lb would do two steps 20% and destroy 80%.
Obviously a bigger bridge or better construction changes these numbers.
Anyone with an erudite SWAG?

Thanks again

Joe