View Full Version : Oleg---An idea to improve skip bombing

10-28-2004, 09:13 AM
It has been said that delayed fuses still do not work vs ships. I realize that PF isn't a ship sim, and additional ship simulation isn't going to happen.

How about this, instead.

Make a new loadout for the planes that usually skip bombed. So you'd see "4x500, 6x500, 4xskip bomb, 1xtorpedo" (or whatever). The "skip bomb" loadout would be otherwise normal 500lb bombs.

The "skip bomb" would damage a ship at the exact same level as a normal 500lb bomb, but would have a greatly reduced blast range vs aircraft. That way you could drop, and fly right over the ship as the bomb blew up. Not realistic, but in real life you WOULD fly over the ship, and the bomb would blow 4-5 seconds after you passed. Seems like a decent compromise to me.

Give it some blast, just less to make it less exact a thing (right now in AEP, I can make the glass nosed B-25s skip bomb, but if they drop even a little too close, they get blown to bits because of the lack of delay).


10-28-2004, 10:26 AM
Bump !!!

Bump bump bump !!!

10-28-2004, 10:29 AM
I was thinking:
Damage to ship = 500lb bomb
Blast effect = 100lb bomb (or maybe less, like a 30kg)

Enough to keep you from doing unrealistically low attacks, but not punish a historical attack profile.


10-28-2004, 02:54 PM
Did they really use 4-5 second fuse?? What if the bomb doesn't penetrate the hull on a side impact?... Then it just sinks for 4 seconds and tickles the ship with a lot of bubbles.

I always thought that the bombs would lag behind the plane since they slow down while skipping and then the ship itself would shield the aircraft from the blast effect... But that's just inexperienced speculation on my part.

Anyone know with some authority how this was done?

10-28-2004, 03:18 PM
A bomb thats sunk after a few seconds would act like a depth charge. Imagine a 1000lbs depth charge go off right under the hull of a ship, wouldn't be pretty.

The 9250lbs bouncing bomb which acts like a depth charge is enough to blow a hole in a 140ft thick dam if thats anything to go by. A Grandslam from 40,000 ft has the same destructive power as that vs a dam. Just something to go by I guess.

10-28-2004, 03:34 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by WOLFMondo:
A bomb thats sunk after a few seconds would act like a depth charge. Imagine a 1000lbs depth charge go off right under the hull of a ship, wouldn't be pretty.

But 4-5 seconds of sinking is a _long time_... that's not the same is going off "right under the hull".

10-28-2004, 03:38 PM
The standard fusing for the 5th AF was 4.5 seconds for skip bombs from what I can tell. The reccomended plane spacing for such attack was 9-11 seconds for this reason.


10-28-2004, 03:51 PM
Hmm, it sounds like you're pretty confident in that fusing time so I take it you're reading it from some credible reference...

Well, I know that a lot of warships had very tough armor on their sides (to resist shell penetration of course) so I'm pretty sure that skipped bombs would not penetrate such a hull. Maybe it would be suicide to fly a skip-bomb approach against such a ship anyway (at least torpedo planes can bank away some distance form the ship)... So then perhaps skip bombing was generally only used on lighter vessels where it was pretty much guaranteed that the bomb would penetrate the side and stick inside the ship?

I have a book (Jablonski) with a series of shots of B25's skip bombing a frigate to death. Presumably such a light ship relied more on size and agility to evade shelling damage rather than have any hope of armor defending it adequately...

10-28-2004, 04:16 PM
The most typical target for skip bombing was merchant shipping, not warships. the "frigates" you see in pictures are probably sub chasers (IJN didn't have a frigate class). These are small ships, 1000 tons and under.

Some online refs:

From an orientation guide...
"f. In skip bombing with regular GP bombs a 4/5 sec. fuse is normally used. This requires the flight or flights to bomb line abreast or with an extended interval to prevent flying through bomb bursts from previous drops."

"O'Dair: OK. You go down, pretty low to the water; you're probably within 30 or 40 feet of the water. And you drop your bomb, and the bomb actually skips across the water because of the forward velocity. And what you have to do is put about a four-and-a-half-second delay fuse in that because you don't want the bomb going off under you. And you have to be careful if you go after an empty ship, because that bomb could go in one side and right out the other. Because, see, ships usually only have a quarter-inch plate. And an empty ship, you'd go right through the hull with that, into one side and out the other. And it could go off underneath you. So you'd try to pull up, soon as you release, you try to pull up and get away; bank away from it."

"Practicing against a ship hulk near Port Moresby, his pilots became adept at low-altitude skip bombing, using five-second fuzes for safe escape. (Although skip bombing was originally devised for B-17s, B-25s and A-20s took over this role because of their better maneuverability.)15 Kenney authorized installation of eight fixed, forward-firing .50-caliber machine guns in B-25 "commerce raiders," as well."

"Kenney recalled: "It looked as though there might be something in dropping a bomb with a five-second-delay fuze from level flight at an altitude of about fifty feet and a few hundred feet away from a vessel, with the idea of having the bomb skip along the water until it bumped into the side of the ship. In the few seconds remaining, the bomb should sink just about far enough so that when it went off it would blow the bottom out of the ship. In the meantime, the airplane would have hurdled the enemy vessel and would get far enough away so that it would not be vulnerable to the explosion.""

This last bit is interesting. I think it implies that the fuse goes off from hitting the water itself, and the delay includes the skipping time. Not sure about this. I do know they prefered wide spacing in line astern attacks so the next plane wouldn't get a bomb in the face (I have pictures of mistakes in this).


OTOH, General Kenney claims instantaneous fuses were used after trying delays for a while in his book (though it has a feww odd claims as well).

10-28-2004, 04:34 PM
That's some cool stuff there... thanks for the references.

10-28-2004, 05:32 PM
Have recently read a book describing RAF Blenhim bombers anti ship missions, they used an 11 second delay.

10-28-2004, 06:28 PM
Just to add some more grist to the mill, a few definitions:

Arming delay: the delay between the bomb being released, and it becoming "live". Bombs impacting before the end of the arming delay will be duds (this is done to ensure safe-escape for the bomber by avoiding detonation following a release below minimum release altitude, or from the bombs clunking into each other under the bomber.) This is not currently available in Il-2/FB/AEP. The bomb is armed at release (sporty!)

Functional delay: The delay between impact and weapon detonation. This is the delay we currently have in Il-2/FB/AEP (and PF as far as I know.) IRL, we use this to determine how far the bomb will bury itself before detonating. Useful for bridges, bunkers, bridge abuttments, and earthen dams.

Timer delay: A simple timer that detonates the bomb at a set time after release, regardless of whether the bomb has hit anything, or hit many things. Most similar to a hand-grenade fuse. I've never dropped something like this, but it sounds like what Tater's sources are referring to.

With the timing delay, if the bomb lodged in the ship, bad news for the ship. If it broke up, or went off low-order (the explosive self-detonated due to impact, instead of the fuse), it was the ship's lucky day. If it bounced, and sank under the ship, still bad news. Any hydrodynamicists out there can calculate the bomb drop distance in water, but figuring 2-3 seconds of skipping, it won't be far. Some torpedoes with similar sized warheads were designed to travel under the target ship and detonate (with varying degrees of success.) They were sometimes refered to as "keel-busters". Tater's suggestions sound like a good compromise, provided the code will support it.

Tater, thanks for the references, and sorry we missed out on the airshow season this year. I wanted to get to the CAF show at Midland, but the cost of our recent greyhound adoption put the kabosh on that. There should be something local in the spring though. Anybody in Albuquerque stocking PF yet?

10-28-2004, 07:44 PM
Not that I've found. And I've looked. Actually, they have it at Best Buy in Farmington according to their web page, lol. A bit of a drive, heheh.


10-28-2004, 07:48 PM
Rog, thanks. If you're looking for me, I'll be the one with the glazed look in my eyes, salivating next to my mailbox waiting for a package from Magnum PC. Be kind and put an umbrella over me if it starts raining, would you?

10-28-2004, 08:30 PM
LOL. I'll be the guy holding a cute 1 year old girl dreaming that if I get it, I'll actually have some time to play it, heheh.


10-28-2004, 09:04 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Blottogg:
Just to add some more grist to the mill, a few definitions:

Some torpedoes with similar sized warheads were designed to travel under the target ship and detonate (with varying degrees of success.) They were sometimes refered to as "keel-busters". Tater's suggestions sound like a good compromise, provided the code will support it.


(The Keel-busters) Never heard of that term used.
From my reading it was just stated the torpedo was designed to break the ships back.
Just playing with words,but if you are digging around for information it might matter.

10-28-2004, 09:08 PM
One added note
Breaking a ships back by detonating under it reguired less of a charge then hitting it in a normal fashion.

10-28-2004, 09:26 PM
Actually the problem with the US torpedo detonators of the time was exactly this. They had magnetic pistols, and were designed to explode UNDER the target, not hit it on the side. The triggers didn't have the kinks worked out, and they wouldn't blow. The older contact fuse torps were fine.

The 4.5 second delay I constantly read about makes much more sense if the bombs start counting moments after they hit the slipstream. they'd eat up a couple seconds skipping, then either go right into the thin merchant ship, or hit, then sink a little.

Since Il-2 doesn't model penetration vs ships I think, the idea of applying damage to it, while limiting the air-blast effect seems better and better. It'll help on oddball drops that just blow when they hit the water as well (if your alt/speed is even slightly off, the blow the second they hit the water and shred you).

On a semi-related note, how does the AI deal with being tasked with a 15m bomb delivery, it sure doesn't like it in AEP, but it is REQUIRED for skip and parafrag bombing to be remotely realistic. The torp planes get in low, right? So there is hope the skip bombers might. If they don't, the separate "skip bombing" ord has an added benefit---the AI must be able to tell level bombing from torpedo bombing, otherwise avengers and kates (and bettys, etc) would pop up to a safe bombing alt at the waypoint before drop (the G and H 25s do this now in AEP when i try and make em skip). This means that behavior must be tied to "torpedo", or "not torpedo". this suggests they could borrow some torpedo-bomber behaviors for skip bombing (it's just an ultra short ranged "torpedo drop" at high speed).


10-29-2004, 11:22 AM
OK, got PF today.

AI is the same skip bombing-wise as AEP.

After watching some torp runs by AI, I think this could work for skip bombing. All they need to do is make the new bomb type I suggested for the air-blast issue and lack of delay, and tell the AI that this loadout requires a torpedo-like delivery, only closer and faster. ~400kph at the same alt as a torp drop. I'll do some experiments with planes layed out next to a static target so I know exactly how far away you have to drop.


10-29-2004, 02:08 PM
Skip bombing is arcade and I doubt has any historical fact other than the dam buster. Most air dropped bombs in WWII were likely armed by an impellor and impact initiated via a point detonating fuse or impact inerta creep spring. The bomb could't tell the difference between hitting the ground or water. A bomb hitting the water is like hitting pavement. They don't delay and explode. At least in WWII they didn't.

10-29-2004, 02:41 PM
sorry, soak, skip-bombing is not "arcade," and I've been asking for it to be made more realistic since FB came out. Now that we have the planes most-used for skip-bombing during the war, but not the speed to escape the blast, we'll really start to see the discrepancy between game and history.

This B-25 ain't bombing the ocean for fun:


You can see splashes from the skipping bombs in this one, and a ship going up in flames in the background:


The hoped for result:


10-29-2004, 03:20 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Soak_:
Skip bombing is arcade and I doubt has any historical fact other than the dam buster. <HR></BLOCKQUOTE>

Skip bombing was used heavily in WWII against light shipping. Check out the articles Tater referenced earlier in this thread.

10-29-2004, 07:03 PM
Bumping this thread

Skip bombing was a commom pratice in the pacfic.
This should be put under a microscope till a fix is found

NO PF hunting it down tomorrow

10-29-2004, 08:41 PM
Skip bombing was the PREFERED method for attacking shipping in the pacific by Army air forces, and was extremely effective. It was the standard attack profile, not an occasional one, level bombing was almost completely ineffective vs shipping, and the Army didn't have loads of dive bombers.


10-30-2004, 12:45 AM
Soak, you're right that water impacts are similar at high speeds to concrete, but the deceleration that normally triggers impact fuzes is longitudinal, not lateral. Tater mentions bombs going off on impact if the parameters are off, and this is because there's enough of a longintudinal component to the impact to trigger the (instantly armed) bomb in the game. Whacking the side of a bomb (usually) wouldn't set it off, or would set it off low-order. I've done a little reading about the explosives used, and while the TNT of early bombs was pretty stable, the RDX was more twitchy (I wouldn't want to skip these IRL.) A mixture of the two (along with powdered Aluminium and beeswax!?!) called TORPEX, was the best combination of blast and stablity.

FWIW, I've dropped live Mk82 500lb bombs (filled with H-6 or Tritonol, more stable than TORPEX), and had the distictly uncomfortable experience of having only 5 of 6 live bombs come off high-drag. The sixth "went slick" and slammed into the water directly under me (we were bombing on a tiny island range off Okinawa.) Luckily, the bomb didn't arm (the fuze was wired to the high drag ballute), and the explosive didn't detonate low-order, it just splashed. With the parameters of the drop, had the fuze armed, it probably would have detonated on impact with the water. I don't recommend snorkling in the waters off this range, in any case.

Owlwatcher, I haven't been able to find any specific references to designing magnetic fuzes to intentionally break keels, but remember hearing about this as a design feature. Going under the torpedo belt definitely makes more sense than trying to punch through it. Perhaps the term was propaganda from my (very brief) stint as a Midshipman, or just History Channel pseudo-information. I also remember seeing footage of a modern Mk-48 ADCAP going off under a target ship, and literally lifting the middle of the ship out of the water while the bow and stern stayed wet. Now if I could just find that footage on-line somewhere... My Google skills are showing their limits.

Regardless, were a bomb with a fixed timer delay to hit the side of a ship, then sink for a few seconds, the effects would be bad for the ship. Hydrostatic shock would be devastating to the hull (even if armored, the armor didn't extend all the way under the ship to the keel, and standard hull plating would be hard pressed to hold out the overpressure from a 500 lb bomb going off ~ 20 feet away... grenade fishing on a very big scale.) Good news for the dropping aircraft is that the water would keep most of the blast from going back into the air, and what made it would be going mostly straight up (path of least resistance) rather than forward to threaten the aircraft (reference the vertical gouts of water in A.K. Davis' photos.) Of course this damage wouldn't be nearly enough to sink a capitol ship, nevermind putting you in the heart of its extensive AAA for a long period. It would be effective against less well equipped ships, as it proved IRL. I'll say again that Tater's suggestion would be a good compromise, if the code can support it.

Edit: spelling, end comment

10-30-2004, 03:42 AM
Just my 2 coins!

I hope it would be possible to model also near miss. Many ships were damaged not by direct hit but by near miss. A bomb falling in the water close to the side of a ship can still damage the ship. The energy of the bomb blast will be more effective travelling in water, while in the air it will be dispersed!

So i think that's why they delayes the bombs for skip bombing pourpouse. 1)First for plane safety. 2)For greater damege.


I read about this in various books, and recently something related in Luftwaffe bomber aces. If Oleg of others of the staff wants i can quote the text.

PS i love Fb, and PF and hope it could become better and better. I hope also someone of the staff could tell us just if it's possible to make in the game code what we are talking of, or if we are speaking trough the wind? http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

PS2 Also the torpedo code needs a big fix (but that's another story...)

10-31-2004, 01:59 AM
Jimmino, thanks for the picture. That's more than I could find on-line with my poor Googling skills. It sums up the various effects nicely.

10-31-2004, 04:20 AM
I asked 1c team about this a while back now.

He111 H6 with 2 x SC 2000kg bombs around 4000lbs
wont even scratch a ship if dropped next to it.
IL2 limitation to shipping is strictly a direct hit only.
Skip bombing as posted earlier with "0" bomb delay is the only way to register a hit.
At present in IL2FBAEPPF you will be lucky to get near any active shipping/carriers due to the flak.
Of course Cargo ships make nice skip bombing targets , as was the practise in war time.
As far as damage caused by skip bombing to your aircraft there is a huge difference in the type of aircraft used.
Fw190 at 700kph will escape unharmed, as will Stukas at 450 kph but some of the PF planes take severe damage from PF shipping on the impact and explosion of the bomb, fighters offer the best skip bombing survivability at the moment, and i dont hink it will ever be fixed that the heavier planes survive at slower speeds after skip bombing.

10-31-2004, 07:06 AM
Yeah, I have tried this with many planes now.

Skip bombing started with B-17s, actually, in the SWPA. The whole point of my thread was that with a minor change (a skip-bombing specific load out) they could create a weapon that would damage a ship, but do less damage to aircraft---and without major code rewrites. Without good skip bombing, bothering to model the B-25G, B-25H, and PTO A-20s was a wasted effort. The "strafer" light/medium bombers were concieved as "commerce raiders" and used that way. It would be like making the Il-2, but only having AI for the Il-2 level bomb from medium altitude.


11-01-2004, 12:46 AM
Well I managed to get 3-4 skips out of my bombs giving me a chance to pull away from the target ship.

BTW use the 2xNapalm with the Corsair IV it sinks the Agaki according to one of our squad memebers.

Theres a skip bombing mission and training trk at our site for download. Im compiling a trk with a twin engine aircraft soon.

11-01-2004, 01:59 AM
You don't even need to worry to much about the blast. One skip about 3-400 meters from the ship is fine, as long as you have enough speed, 450-500kph. The AA defending ships is something to worry about.


11-01-2004, 04:29 AM

B25 Skip bombing training tracks done.

It includes a DF map to practise on all our squad use it this has 1 carrier active flak to practise on the rest are asleep.

Just follow the readme file in the zip to install the training track,,,, not that you fellas need any telling lol.

See Missions section in the site link below.

11-01-2004, 06:45 AM

You can also use the onlineislands8/pacific islands as that has a number of ships and subs on it. Crimea also has ships but thats probably more useful for practicing s turns as you come into attack as theres allot of AA.

11-01-2004, 07:55 AM
I can skip bomb as well, but it requires more speed (as you say) than was historically the case (typical was ~200mph---~320kph).

They also need to make it so AI can skip bomb. Seems they could use the torp-plane AI, just go in faster, and drop closer.


11-01-2004, 10:16 AM
a blast under the ship should do a great deal of damage from what ive read.
a 0 delay is on balence the worst, cos u danger yourself greatly, and u wont do internal damage, or below the water line.

i dont think the **** busters had a great deal of explosive, i cant remmber. but they where mighty effective, increadibly so if u compaired to trying todo the same with level bombing

11-01-2004, 02:13 PM
It really shouldn't be that hard to enhance the engine to enable the delayed fuse to work on ships. There would just have to be a special case where the location of the bomb is tracked with the moving ship... essentially the bomb is just flagged has being stuck to a ship rather than stuck at a particular location on the ground.

11-01-2004, 02:35 PM
The AI needs to be reexamined as well. AI won;t skip bomb, particularly with the very planes that did it as a standard attack.


11-02-2004, 12:17 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by AgentBif:
Did they really use 4-5 second fuse?? What if the bomb doesn't penetrate the hull on a side impact?... Then it just sinks for 4 seconds and tickles the ship with a lot of bubbles.

I always thought that the bombs would lag behind the plane since they slow down while skipping and then the ship itself would shield the aircraft from the blast effect... But that's just inexperienced speculation on my part.

Anyone know with some authority how this was done? <HR></BLOCKQUOTE>

Oh YES, I have a book wich is written by a former commander of the 18th (NEI) squadron under the RAAF. this squadron flew B-25 mitchells and did quite alot of skipbombing. Since this technique reduces the effectiveness of AAA. He stated that the bombs had 5 second fuses. The fuze would go running once the bomb hits the ship. The idea is that the bomb would sink and explode somewhere under the ship (maybo on the bottom if the harbour)? and when it exploded, the water between the ship and the bomb would act as a giant force multiplyer. It would smash the ship out of the water and break it somewhere in the middle. This was considered far more efficient then just dropping bombs above a ship.

Furthermore, when I use skipbombing in PF, I race towards the ship and when close, I pull my nose up some 10 or 20 degrees and release the bomb(s) after that. This way, your bombs will fly further and they still will skip on the surface water. While you get some more room to climb to suffiecient altitude. 100 or 150M is allready enough in most situations.

11-03-2004, 03:55 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Tater-SW-:
The AI needs to be reexamined as well. AI won;t skip bomb, particularly with the very planes that did it as a standard attack.


Aye, and the AI should strafe on the way in too (after they make it so you can actually damage or suppress ship AA)!

11-03-2004, 05:08 AM
So is the big gripe here that in the B-25 it is too difficult to skip bomb and pull up unscathed? Because its easy to do it in single seaters. Is that why people wish the delay would work? I dunno, I understand this is a pet peeve of some people, but I hope other things are addressed before this.

11-03-2004, 11:15 AM
My take on priority is that since shipping is such a valuable target in campaigns (as it was in reality), and since skip bombing is really the only reliable way for a B-25 or A-20 to take out a ship (as it was in reality), then this should be a reasonably high priority fix. Without it, B-25 and A-20 campaigns are severely weakened.

A ship-strafing fix is also important for the same reasons (strafing was necessary on the approach to protect the bombers since that approach profile is a dream for AA gunners).

11-03-2004, 12:11 PM
The skip bombing problem is threefold.

One, the lack of delayed fuses (or some stand in) makes it tougher than it should be for light, medium, and even heavy bombers (B-17s and B-24 routinely practiced mast height attacks).

Two, the fact that strafing doesn't supress AAA makes the MG laden strafers semi-useless for their purpose built design.

Three, the AI won't practice either of the above two tactics, regardless of effectiveness or danger.


11-08-2004, 02:33 PM
Found some interesting data points that relate to some of this discussion...

From "Dauntless Helldivers", a book by Harold Buell, an American dive-bomber pilot in the Pacific theater... In a section discussing the issue of near misses where several of them landed bombs right next to submarines without sinking them:

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>A near miss with a depth charge was often better than a bomb's direct hit because it opened a submarine's seams and flooded it. For a general-purpose bomb to be effective, a direct hit before the sub went underwater was required. Once the bomb hit the water, much of its explosive effect was lost due to the muffling effect of that medium. This was true only of small bombs -- 1000 to 2000 pound bombs were known to cause severe damage to the sides of ships by near-miss concussion." <HR></BLOCKQUOTE>

This is curious to me... I am thinking that the US very likely did specific tests to determine the effects of near misses of various types of bombs and of course the specific conclusions of these tests would have been passed on to dive-bomber pilots in training. I suspect that it was determined that a near miss with a 500-lb was just not damaging enough to most vessels while 1000-lb and above was determined to be quite useful.

Buell's comment about 500lb bombs being "muffled" by water seems off to me... I believe that water with it's higher density would transfer concussive pressure more effectively, no matter the size of the bomb. I figure that he is speculating incorrectly as to why the Navy dismisses the 500lb near miss. (Maybe the 1000lb blast passes some critical threshhold of power in it's overpressure wave making it capable of overcoming the integrity of most hull structures?)

I think what we can glean from this is that perhaps 500lb near misses just weren't deemed effective by the US Navy and so if the game ever gets around to modelling near misses, real damage probably shouldn't occur unless the bomb is 1000lb (500kg) or larger.

11-08-2004, 02:51 PM
Coincidentally, I also came across this by Jimmy Doolitle (from I Could Never Be so Lucky Again):

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>The evidence showed how extremely difficult it was to obtain direct hits on an object as small as a gun emplacement even when there was little or no enemy interference. Examination of 80 guns which had been attacked from the air showed that... only two batteries had received direct hits. Inconclusive evidence indicated that in attacks on batteries the effective radius of the US 1000lb bomb was only one and a half times that of the 500lb bomb; hence it was better to use the smaller bomb against pinpoint objectives because of the larger number of bombs which could be employed. <HR></BLOCKQUOTE>

The reference Doolittle is quoting from he cites as "the official history of the Air Force" regarding analysis of operation Corkscrew.

So at least in atmosphere, it seems they deem the double-sized bomb as only half-way more effective against point targets. Intuitively this makes sense to me... You double the energy in a 1000lb bomb, but the concussive effect I think should fall off with the square of the radius from the impact point ... so you don't double the effective radius with the larger bomb.