Sub Skipper's Bag of Tricks

[ColonelSandersLite]

Originally Posted by Barkerov

I would much more easily believe that than bomb damage at that depth from a surface detonation. 40ft sure but 200ft I would need proof to believe that.

Something a lot of people don't realize about bombs is that they generally don't explode on contact and there is a lot of good reasons for this. A 0.1-1 second delay is pretty typical depending on a lot of factors. Fuze delays must be set on the ground before takeoff

Taking the example of a american an-m64 (which is pretty typical of 500 lb/250kg bombs of the era)
Minimum Safe Release Altitude: 1,500 feet
Striking Velocity from 1,500 feet release: 450-750 feet/second (depends on dive angle and aircraft speed! Will be higher from a higher release altitude!)

Contact with the water would slow it down some, but we'll simplify here.
Depending on the delay setting and release speed, a miss will explode at a depth of 45-75 feet with a delay of 0.1 seconds. Similarly, explosion depth would be 225-375 feet with a 0.5 second delay setting. Just like a depth charge, if it is close and explodes underneath you, it could seriously mess up your boat.


Long story short, I advise you dive deep the second you make contact with an aircraft. Though they have to get pretty dang close to spot you submerged at all.

[Rockin Robbins]

And don't forget, they dropped depth charges too. How can you tell from the conning tower whether what the plane dropped was a depth charge or a bomb? And if it kills you did it make a sound?

[ColonelSandersLite]

Now, I remember a fighter pilots account where he spotted a submerged submarine and tried shooting at it a few passes. I don't remember his nationality but he wasn't american so we're probably talking some flavor of .30 cal machinegun. Complete waste of ammo there.

[Rockin Robbins]

Some actual shots of submarine at periscope depth:






There are times where the sub is much clearer than these photos show. I have seen a photo of a nuclear sub from straight up that was really scary in the extreme visibility of the sub, but that was back in 2007 and I can't find the photo now.

[Barkerov]

Originally Posted by ColonelSanersLite

Something a lot of people don't realize about bombs is that they generally don't explode on contact and there is a lot of good reasons for this. A 0.1-1 second delay is pretty typical depending on a lot of factors. Fuze delays must be set on the ground before takeoff

Taking the example of a american an-m64 (which is pretty typical of 500 lb/250kg bombs of the era)
Minimum Safe Release Altitude: 2,500 feet
Striking Velocity from 2,500 feet release: 450-750 feet/second (depends on dive angle and aircraft speed! Will be higher from a higher release altitude!)

Contact with the water would slow it down some, but we'll simplify here.
Depending on the delay setting and release speed, a miss will explode at a depth of 45-75 feet with a delay of 0.1 seconds. Similarly, explosion depth would be 225-375 feet with a 0.5 second delay setting. Just like a depth charge, if it is close and explodes underneath you, it could seriously mess up your boat.


Long story short, I advise you dive deep the second you make contact with an aircraft. Though they have to get pretty dang close to spot you submerged at all.

A 2500ft release is going to have serious accuracy issues and i think the slowing it down some is a bit of an understatement. I recall an episode of mythbusters where they tested if water was bulletproof. Indeed this was plausible but I was especially surprised to learn that the faster the projectile hit the water, the less it penetrated. Furthermore the larger the projectile the less it penetrated the surface tension of the water. So what this means for a 500 pounder doing 0.46 to 0.67 mach is unclear. In any case whatever the AI slants are dropping on me is from well under that height.

[ColonelSandersLite]

Originally Posted by Barkerov

A 2500ft release is going to have serious accuracy issues

That was supposed to be 1500, sorry edited above. Still, I don't know how close you think bombers actually got to their targets. Fuses typically wouldn't let the bomb even arm if released under a thousand feet to prevent destruction of the aircraft. Dive bombers of all nations typically released between 1000 and 3000 feet depending on payload and the aircrafts specific characteristics (i.e. it's ability to pull out of the dive). 1,000 is really point blank range, 1,500 and even 2,500 are not uncommon release altitudes at all.

Originally Posted by Barkerov

I recall an episode of mythbusters where they tested if water was bulletproof. Indeed this was plausible but I was especially surprised to learn that the faster the projectile hit the water, the less it penetrated. Furthermore the larger the projectile the less it penetrated the surface tension of the water. So what this means for a 500 pounder doing 0.46 to 0.67 mach is unclear.

Doesn't mean anything. If you recall, the impact had a tendency to shatter the bullets. If memory serves the correlation between size and effect on the bullet didn't really exist either. Basically every time they went up in size, they where using bigger guns with better muzzle velocities. I'm sure the effect is there to some degree, but their "study" didn't really show it out. General purpose aircraft bombs routinely survived falls of 25,000 feet, smashing through and into concrete and steel, successfully detonating after impact as designed. There where bombing missions with release altitudes of over 30,000 feet as well and again, the bombs functioned fine. At those release altitudes, the bombs where actually going at supersonic speeds on impact. Water is comparatively not that tough. Not even close.

Originally Posted by Barkerov

In any case whatever the AI slants are dropping on me is from well under that height.

That's purely because the game designers knew something about submarines, but not aircraft. Alternatively, they decided to do it the way they did in the name of game balance to give you good odds of shooting down aircraft with the AA guns. The way the aircraft operate in the game is completely and totally unrealistic.

[Barkerov]

I think I am not writing enough words and therefore coming across as an idiot who knows nothing about bombing, fuses etc. Let me start by saying that I know a lot more about aircraft than submarines and that flight sims were my first love of war simulation games. I agree totally that the way the game implements aircraft is unrealistic, the reason you supplied of giving the player a chance is probably spot on, since developers have to cater for the realists and the arcade players equally in order to maximise profit.

I don't think for one second they got closer than the fragmentation envelope of the bomb they were employing. I also am under no illusion that the bomb will fail to detonate after impact with the water becasue of damage to the bomb. After all they are designed to hit the ground at supersonic speeds. Furthermore I am not stupid enough to believe that Mythbusters provide anything more than proof of concept experiments. Your point about increasing projectile surface area / weight being confounded by muzzle velocity is correct. However the key concept, that high velocity impact with the water dramatically changes the projectiles behavior, is valid.

My query revolves around how deep is deep enough both IRL and in the game. I have not seen aircraft bombs with delay fuses yet so the first question is how damaging would a surface detonation be to a submarine at various depths. I suspect not much at periscope depth

The second question, which you got me thinking about, was how deep will a bomb penetrate underwater before detonation. Lets for a second assume that skipping of the bomb is a non issue. My feeling (please note how I distinguish between what I think by using emotive terms and what I can prove as fact) is that the bomb will lose almost all of its airborne energy upon impact with the water greatly reducing the speed at which it travels underwater particularly in the direction of depth. To get to 40ft with a 0.1 second fuse it is easy to see that it has to travel downward at 400ft per second, a value which I find very hard to believe. A half second fuse which you suggested would detonate at 225-375 feet deep would require downward motion equal to the impact velocity. This would defy the laws of physics.

I found a book today entitled "Britain's Anit-submarine Capability 1919-1939" which stated that one report concluded that "for entry velocities of more than 250fps the trajectory curvature may be so great that accurate bombing of submarines at depths greater than 50ft would be impossible". I have probably taken this quote too far out of context but there must be a reason why planes carried depth charges instead of bombs.

[Sailor Steve]

Airborne anti-submarine bombs used by the Japanese generally used a 3-second-delay fuse. The effective underwater range was given as 10 meters, which makes it about as powerful as an extra-large depth charge, and no good at much more than periscope depth.

Naval Weapons of World War II, by John Campbell

[TorpX]

Originally Posted by Barkerov

The second question, which you got me thinking about, was how deep will a bomb penetrate underwater before detonation.

I have no idea how deep a bomb in the game can go, or how that is determined, but I think as far as our safety is concerned, it is more a problem of how large the blast bubble is, than exactly where the bomb goes off. And of course, how deep can they see us.

I did some tests after having some experiences like yours (with RFB + RSRDC), and found that it was possible for a low flying a/c to see and kill me at 200 ft. Granted, he was flying right over me, and low, but I thought it a bit much, and decided to edit the files to prevent that.

If you want to do this CapnScurvy explains how to do it HERE. You would need to change all the airborne sensors for this.

[Barkerov]

Originally Posted by Sailor Steve

Airborne anti-submarine bombs used by the Japanese generally used a 3-second-delay fuse. The effective underwater range was given as 10 meters, which makes it about as powerful as an extra-large depth charge, and no good at much more than periscope depth.

Naval Weapons of World War II, by John Campbell

Thankyou sir
That answers my second question completely.

[Aktungbby]

Originally Posted by Barkerov

To get to 40ft with a 0.1 second fuse it is easy to see that it has to travel downward at 400ft per second, a value which I find very hard to believe. A half second fuse which you suggested would detonate at 225-375 feet deep would require downward motion equal to the impact velocity. This would defy the laws of physics.

The teardrop-shaped United States Mark 9 depth charge entered service in the spring of 1943. The charge was 200 lb (91 kg) of Torpex with a sinking speed of 14.4 ft/s (4.4 m/s) and depth settings of up to 600 ft (180 m). Later versions increased depth to 1,000 ft (300 m) and sinking speed to 22.7 ft/s (6.9 m/s) with increased weight and improved streamlining. Roughly 5 seconds per 100 feet. Note the sink times: http://www.ussslater.org/tour/weapons/dpthchrg/dpthchrg.html And then watch out for serious hunting from the air in 'follow-on' attacks http://www.ibiblio.org/hyperwar/USN/rep/ASW-51/ASW-13.html

Originally Posted by Barkerov

I have probably taken this quote too far out of context but there must be a reason why planes carried depth charges instead of bombs.

Footnote to history!: The first to deploy depth charges from airplanes in actual combat were the Finns. Experiencing the same problems as the RAF with insufficient charges on anti-submarine bombs, Captain Birger Ek of Finnish Air Force squadron LeLv 6 contacted one of his navy friends and suggested testing the aerial use of standard Finnish Navy depth charges. The tests proved successful, and the Tupolev SB bombers of LeLv 6 were modified in early 1942 to carry depth charges. The success of the anti-submarine missions reached RAF Coastal Command, which promptly began modifying depth charges for aerial use. [wiki] Thank heavens there were so few Squids: note the sink rate: Squid consisted of a pair of three-barrel mortars whose pattern of six depth charges was normally fired dead ahead, but could be trained 30 degrees to the sides if warranted. Each charge weighed 390 lbs (177 kg) of which 207 lbs (94 kg) was minol. These had a sinking rate of 43.5 feet per second (13.3 m/s) and the fuses operated by clockwork. The pattern was overlapping triangles 40 yards (37m) on a side with the depth of the triangles set 60' (18m) apart. Squid was equipped with a fire control system that was tied directly into Type 147 sonar (no 'blind spot') and automatically set the detonation depth and fired the charges from the mortars at the right moment. It was estimated that Squid was nine times as effective as a conventional depth charge attack, or over twice as effective as Hedgehog, with about a 40.3% probability.

[TorpX]

Very interesting about the Squids there, Aktungbby.

[Aktungbby]

Originally Posted by TorpX

Very interesting about the Squids there, Aktungbby.

JA! VERRR....

[Rockin Robbins]

Awesome information, Aktungbby. Over 40% accurate and the 1 knot silent running speed of the U-boats meant the Atlantic was safe. Except for the U-boats!

Well, the stuff on the surface was safe, anyway. The only thing a sub could do about that attack was run out from under it and I don't even think a fleet boat could have done that. A Guppy II might have, but wow! Talk about a game changer...

[Aktungbby]

I just can't believe the math in the OEG link http://www.ibiblio.org/hyperwar/USN/rep/ASW-51/ASW-13.html of hunting techniques percentages from the air. Now I gotta worry about a 'reconnect' on my 'gambit course'. Reading Black May and seeing the Movie: A Beautiful Mind are required forers. Really, once the science jocks discovered transit time across the Biscay Bay and U-Boat battery-endurance limits, the jig was up. the Triton version enigma of the Kreigsmarine and Dönitz's adding fourth rotor-wheel didn't give the Allies all that much edge in real time. I'm taking some aspirin and getting out my old trig tables:

The "entrapment triangle" is drawn tangent to the sonar detection circle with limiting escape lines drawn at angle = sin-1 sub speed/ship speed. In this way it is analogous to the submerged approach zone except that the submarine is trying to get out rather than in. As can be seen from Figure 1 searching in line abreast makes such evasion impossible except from positions near the ends of the line. Some theoretical considerations concerning search in line abreast arc given in Chapter 6, Volume 2B.
There are also many practical reasons for searching in line abreast. The ships are close enough for convenient communications and know the positions of their fellow ships at all times. Similarly the ships' are readily recognizable by aircraft or other forces in the area, even at night. In addition ships are in a position to coordinate during attack once a contact is made.

MEIN GOTT!! I thought Einstein was working on the bomb! They're hunting me with math; never mind what they'll actually kill me with!