Could a 120mm mortar shell with an armor piercing shaped charge warhead, be able to penetrate the pressure hull of a submarine? I was just thinking that while a large depth charge will destroy a submarine, it needs to be fairly close. And airplanes only had a couple to be dropped. But, what if you could drop hundreds of them at once? Most would miss, but it would only take one to do some damage.
I compared it to the Hedgehog and it seems to be half the weight, but perhaps a AP shaped charge might still get the job done. It might depend on the Sub as well.
I think it would also depend on the depth of the sub. A .50 caliber round only penetrates a few feet of water before it loses velocity - if I remember correctly. A mortar round would most likely not go too deep. A sub on the surface would be another matter though. edit; just reread this and duh!!! Mortar round would fall all the way to the bottom wouldn't it?
Perhaps that answer is not readily available for latest subs.....however the subs of WWII would probably be vulnerable to that size of round depending on where it was to hit.
edit; just reread this and duh!!! Mortar round would fall all the way to the bottom wouldn't it? - Well yes, but it may disintergrate upon impact...The problem with sinking a sub, was not the ordnance so much as actually hitting it. The Hedgehog would be considered a "mortared" round. A 120mm mortar round WOULD breach the pressure hull...fairly easily. The pressure hull is like "cast iron" in that its about strength against a consistant pressure application...its "brittle" against fast, pin point pressure and will crack fairly easily. Pretty much 20mm and above should get a Submariner very concerned...in my opinion. Anything decent should damage a WW2 sub from about 60 feet away...pressure!
Biak and CAC are on the right track although they don't seem to know it. The mortar round will go all the way to the bottom, but we need to find out two things A.) A shaped charge will have a "gap" to allow for the molten metal jet to properly form...At what depth will this hollow area collapse under water pressure - thus negating the effect of the shaped-charge. B.) We also need to know the sink rate of the 120mm mortar round - faster the better. The older DC's had a sink-rate of about 5-10 feet per second, later DC's upped it to about 20-30 feet per second - with the hedgehog somewhere around 22-23 feet per second. Another problem I would foresee is that all the U-boat had to do to be safe was put the rudder hard over, since the aircraft can't drop the mortar rounds in a pattern(like the hedgehog), but could only drop them in a straight line.
Okay now ya' got me thinking about this. Could say a squadron of TBF Avengers each drop a full load 20-40(?) 50lb contact 'grenades' (for lack of a better word)? Flying abreast they theoretically could lay out a pattern X by X yards. Something along the lines of 'parafrag's.
Takao, Isn't the same problem incurred with conventional dropped Depth Charges, Rockets and Cannon's? Granted the last two were quicker on target, but would not a string of these launched from a single aircraft attacking at any angle other than dead on have a fair chance to straddle the target? As always, countermeasures would depend on the sub surviving the attack, correctly deducing the nature of the attack, reporting the new type of weapon, and finally convincing the ''Brass", that it is not all the imagination of skittish sub commanders. I seem to recall that the "Brass" all too frequently dismissed reports from Sub commanders that contradicted tactical policy or the effectiveness of weaponry until reports began to flood in, or alot of sub began disappearing without apparent reason.
"Another problem I would foresee is that all the U-boat had to do to be safe was put the rudder hard over, since the aircraft can't drop the mortar rounds in a pattern(like the hedgehog), but could only drop them in a straight line." - Yes, present the sub as perpendicular to the attacking aircraft...he will try to come up your length...The pilot can line up the sub pretty easily its the drop of the bombs...the "length" not the line thats the problem. Running up the length gives the pilot a hundred feet or more to hit the sub...side or perpendicular its the sub's width, about what? 8-12 feet? However....the Sunderlands would run their bombs across the wings, and time the realease shortly after the next...giving a foward and sideways stream of bombs...
But CAC, if an aircraft can drop a pattern of "n" number of small shells over a grid of x feet by y feet, the probability of a hit would be pretty high. I'm wondering if smaller bomblets, of which many can be carried, could be a sub killer.
Indeed! Increase the chances for sure...The Sub commander can only put on full knots to increase the calculation diffculty...A commander really "should" dive like a bastard on first "hearing" an aircraft...but one can get caught out for a number of reasons. Small bomblets are a really good idea...one doesnt have to destroy a WW2 sub...just render it impossible to dive (either damage its dive planes or crack the body somewhere)...
A shaped charge designed to kill a tank would easily penetrate a sub's pressure hull. But only if it hit the hull directly. The "skirts" the Germans developed would have their counterpart in the decking on a U-boat, in my opinion. The hydraulic kill is more reliable, you don't actually have to make contact, and if you do, the shock of the detonation will be transmitted to the hull.
I don't view the idea as very practicable or successful. Armor piercing would not work; your most likely kills are from hydraulic forces (larger explosion and shockwave) or shaped charge, which I actually don't view as that likely to succeed. As Opana pointed (rimshot!) out, most of the WWII subs had a deck above the pressure hull. That deck and the water in between would serve as armor, diluting the strength of the jet formed by the shaped charge. Getting multiple aircraft to fly in strict formation to drop accurately would be difficult; they would need to form up and dive in unison; in order to do that before the sub crash-dived they would likely need to patrol in formation, which would decrease the amount of area a group of aircraft could cover. I would think that it would have been more useful to develop something akin to the JP233, but that type of device would have been only usable by aircraft of the Avenger/Tarpon size or larger.
