Most effective "possible" WWII weapon at sinking merchantmen?

I think you seriously over estimate the effectiveness of puny 40mm round to do damage to a large steel built ship. Yes a small wooden vessel the size of a trawler (say 150tons) would in all likely hood receive terminal damage if subject to a sustained attack by 40mm gun armed aircraft. However a five to ten thousand ton merchant vessel is a whole different story. Just look at some of the after action photographs of SS. Brisbane and the Tanker Ohio from the Pedestal convoy to see how tough a target they were to sink. Any merchant ship has a hull divided into water tight compartments and pumps designed to discharge significant water ingress. Though not in the same class as naval damage control all merchant crews were capable of damage control. As long as you can get to the damage a hole punched by a 40mm round can be sealed by hammering a simple wooden bung into the hole. If the hole is unreachable fro inside then it or even a group of holes can be patched by fothering (placing a canvas or rope pad over the outside of the hole) a tried and tested method that has historically been used to repair significant damage.
There is good reason for the saying. " to let in air use a gun, to let in water use a torpedo".
 
That might be a correct spotting, as I do recall clearly that the phrase did include 'all shipping', so do you think that this rather sweeping statement has given me, a two generation removed Yankee, a mistakenly drawn conclusion about the water off the UK in summer/early fall 1940? I don't mean within 200 miles of the shore, by the way, as that is within the range of any and every fighter in the UK, and so not a good place to send a 'ship hunter' group.
f0516.jpg

That's a very helpful map showing the distribution of British-flagged merchant shipping in about 1937 or so. Apart from showing just how badly the British were hit by Italy entering the war (all that trade through the Med had to go around the Cape instead - at least five times the distance), it also shows what a low fraction of their ships were in the Western Atlantic at any one time. Even if you convoy everything from Freetown and New York/Halifax on the way in and disperse the convoys once out of danger on the way out, there's a huge amount of shipping that is simply out of range of anything but a surface raider.

Why do you keep comming back to the 75mm?
Because it's the biggest gun you list in your OP, as part of the armament of the B-25?

And the 88mm was 'rubbish'? Why then did it start out as the preferred method of sinking a merchantmen at the outset of the war? And the 88 was to be used on a stationary ship, and fired from (for all intents and purposes) from the surface? I don't know how it stacked up against a cruiser's guns, but in terms of being cheaper to expending a few rounds rather than expending a torpedo, that trade off seems clear.
It should be noted that the German torpedoes weren't very good at the start of the war either, and that lobbing a few 88mm bricks at a merchant ship only works if it's unarmed. As soon as they can shoot back, the submarine is out of there because it's a sitting duck if it gets damaged and can't dive. You also need to hit exactly on the waterline if you're going to sink something, and that's harder than it sounds (a submarine is NOT a good gun platform).

I am, of course, going to make the assumption (yes yes, an assumption) that your fathers ship never sailed on that run alone and came under air attack, so that the 11 AA guns were never put to the test, inasmuch as there would probably always be a warship in escort with AAA, right?
Err... what? You've got the Luftwaffe attacking a convoy, and you are going to have your AA gunners sit there with a certain digit up a certain orifice because there is a warship about that also has guns on it? If you're under attack, everybody is going to be shooting back.

I have to ask a relitively simple question here, how much seawater will enter an unplugged 40mm hole per second?
Not a lot. Critical point here you seem to be missing - an aircraft is aiming at the ship as a whole, not just the waterline (and will almost certainly be shooting from a considerable distance). You sink ships by making holes that let water in, not that let air in - the overwhelming majority of holes from a strafing attack will be far above the waterline and merely make the place a bit better ventilated. Those aimed far below the waterline will be stopped by the water and won't penetrate. You've only got a small zone that is sometimes above and sometimes below the waterline, and that means any holes will sometimes help drain the compartment, and will never be under very much water pressure.

If the dual purpose AP/HE round detonates in a confined, watertight compartment, odds are it will no longer remain watertight. Does the detonation blow the door (hatch) right off, or mearly make twisted wreckage of it?
Where do you get 40mm from? The BK37 HE round was 640g, and around 10% of a HE shell would be high explosive (65 grammes or a whisker over 2 ounces). If you've ever been on a ship, you'll know that they're pretty heavily built - 2 ounces of high explosive isn't going to blow the doors off. Kill everyone in the room, almost certainly. Smash up any delicate equipment, yep. Distort a door, possibly - but blow it off? No chance.

All I can say is, "REALLY"?:eek:
Yeah. If you're attacking out of fighter range of the UK (and remembering that the convoys were routed a long way north to avoid exactly this sort of attack), you're out of range of anything fast and nippy that can hope to attack into a flak barrage. You end up with converted airliners like the Condor, which are very large and have many vulnerable points. It doesn't take much damage to an aircraft that still has 1,000 miles to go home to ensure it won't make it back to base - and if it doesn't, it's an awfully long way for the crew to swim...
 
Because it's the biggest gun you list in your OP, as part of the armament of the B-25?
See (meaning: re-read) post #12.

Err... what? You've got the Luftwaffe attacking a convoy, and you are going to have your AA gunners sit there with a certain digit up a certain orifice because there is a warship about that also has guns on it? If you're under attack, everybody is going to be shooting back.

I guess I should clarify that one. The point was not that the 11 AA guns (as well as every availible gun in the convoy), would for some reason not fire, but rather that, as had been prevuiously posted, that they alone would provide an adaquet AA defense. That was what I was calling out on. I guess I worded that badly.:(

Not a lot. Critical point here you seem to be missing - an aircraft is aiming at the ship as a whole, not just the waterline (and will almost certainly be shooting from a considerable distance). You sink ships by making holes that let water in, not that let air in.
As above, re-read post #12.

the overwhelming majority of holes from a strafing attack will be far above the waterline and merely make the place a bit better ventilated. Those aimed far below the waterline will be stopped by the water and won't penetrate. You've only got a small zone that is sometimes above and sometimes below the waterline, and that means any holes will sometimes help drain the compartment, and will never be under very much water pressure.
I'll wait for someone that actually has the physics, to explain that one.
Perhaps at this point, I should ask you to explain the attack profile as YOU envision it, because your posts don't seem to match what I posited as the attack profile.

Where do you get 40mm from? The BK37 HE round was 640g, and around 10% of a HE shell would be high explosive (65 grammes or a whisker over 2 ounces). If you've ever been on a ship, you'll know that they're pretty heavily built - 2 ounces of high explosive isn't going to blow the doors off. Kill everyone in the room, almost certainly. Smash up any delicate equipment, yep. Distort a door, possibly - but blow it off? No chance.
In the OP, some info was provided to me by another user, the rounds were something like 1.96 lbs. I just rounded that off to a nice, even 2 lbs. At 32 oz total weight, and following your formula, this would not result in a 2 oz charge, but rather a 3.2 oz charge. So an explosive 1.6 times more powerful that what you posted.

Of course, we are dealing with a weapon system that doesn't really exist, and so extrapolation will be needed no matter what OTL weapons we try to look up. For instance, this weapon we are talking about needs to be (relatively) light weight and compact to be used from an aircrafts belly turret (As posited in post #12), but perhaps its ratio of explosives would be different, based upon experimentation at the time, what with the weapons intended role was going to be.

Yeah. If you're attacking out of fighter range of the UK (and remembering that the convoys were routed a long way north to avoid exactly this sort of attack), you're out of range of anything fast and nippy that can hope to attack into a flak barrage.
Lets see, post #12 (again), and please provide YOUR attack profile, since you once again seem to be missing/ignoring mine.

You end up with converted airliners like the Condor, which are very large and have many vulnerable points.
The whole thread is about an ALTERNATE Germany, and its ATL warplans, and the ATL forces that it designes for the purpose.:confused:

It doesn't take much damage to an aircraft that still has 1,000 miles to go home to ensure it won't make it back to base - and if it doesn't, it's an awfully long way for the crew to swim...
This part is both true and unavoidable, both in OTL and in any ATL that I can concieve of. OTOH... (not in this thread, I think)

Your map seems to indicate a large amount of traffic heading north/south from the UK.
 

Sycamore

Banned
By the way, didn't the B-25H carry a 75mm cannon? With Henschel Hs 129B-3 ground attack aircraft and the Junkers Ju 88P-1 also carrying 75mm Pak 40 guns? And what if something akin to the Lockheed AC-130 were developed earlier, using a larger caliber weapon (say, an 88mm Pak 43), mounted to be fired out of the side of the aircraft while it circles its target in the same fashion (thereby enabling it to try and skirt around an AA flak barrage rather than flying head-on directly into it)?
 
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Saphroneth

Banned
The described attack profile (low and level) is the kind of thing AA barrages find easy to take out. OTL 20,000 feet was not really high enough to be safe from AA, here you're coming in at 1,000 feet height and 1,000 yards range which is high enough to not get cover from the waves but easily within effective range of every gun fitted - including the machine guns.
As for your description of how they'll use the machine guns to "walk" their fire...

First, machine gun bullets and heavier rounds have different ballistic properties. The only people in history I know of who could do this were the superbly trained aviators of the 1st Carrier Striking Force with their Zero guns (aiming the 20mm cannon with their machine gun tracers) and they were too well trained - the opportunity cost if one of them was lost was too high.
Second, from over half a mile away and you're expecting them to see exactly where their machine gun bullets are hitting a ship down to the right two or three metres? What the heck?

Finally, no-one is claiming that the AA guns will score perfectly. Just that, in the length of time it takes to sink a merchant ship with the weapons you describe, the AA guns will have been able to hole a fuel tank or damage an engine or do something to compromise the ability of the aircraft to fight on - which is a bad thing when your flight plan involves flying up past Norway, west around Scotland, south past Ireland and then getting into the shipping lanes.
And - and this is the important bit - you have to plan that because you cannot rely on getting bases on the French coast.



 
If you Google Defensivly equpped merchantmen you will find most of the answers you seek.
I wish I could, but as I posted upthread, google no longer supports either win XP nor IE8, and even when I installed firefox, the google site still won't come up.:(

For the Germans to make a significant attack on merchant shipping after the fall of France they would have to invested pre war in a long range bomber.
Yep. Hence this thread.:)

After the fall of France most shipping to the UK was routed to the north of Ireland.
This I would assume was the shipping going back and forth to N america? Was the shipping going to S america likewise being diverted in such fashion? And what about that which was going around S africa?

In real life the fitting of. 20 mm cannon discouraged low level attacks from the few Condor aircraft available.
Yes, but this thread isn't about OTL Germany, that didn't make (let alone carry out) a comprehensive plan for the defeat of the UK, but rather an ATL Germany that does.
 
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Saphroneth

Banned
ATL instead of OTL doesn't mean that their aircraft are suddenly immune to 20mm cannon fire.

As for shipping routing - yes, they routed around the areas of greatest threat, meaning the eastern Atlantic around the French west coast.
 
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The artic convoys were beefed up with AAA and the guns were manned not by "my Grampa" but by men like his brother (my Great Uncle) who was seconded from 5th AA Division who completed his war landing with the 11th Armoured (D+7 Epsom, Goodwood, Bluecoat, Market Garden and liberating Bergen-Belsen).
This part is good information, for which I am glad and pleased to have, as without you post I likely would never have known it. It is also relevent to this thread, and therefore both on topic and appreciated. Thank you.

This other part I will only respond to once.
I come here, to the alternatehistory.com forums as a hobby, and strictly for entertainment purposes. I don't generally make it a habit to deliberately insult, nor provoke, my fellow forum community members.

So for this part, let me start off by saying, if I have offended, then I hereby and publicly appologise for any and all offense taken.


I find your assertion quite insulting on two levels:
Allow me to explain. First, this was not intended as an insult, nor an assertion of any kind. It was in fact a two part joke. Back in the day, while serving in the US army of occupation of Berlin, I often had occasion to play a game with my comrades in arms called 'axis and allies'. On numerous occasions, a player would engage a sole enemy transport (that has but 1 chance in 6 of scoring a hit), with their bomber (which has a 1-4 chance of scoring a hit), and not only fail to hit the transport, but getting shot down by it. The simple math odds of that are something like 18:1, but it happened often enough in our games, that the standing joke went something like, "Grandma, with her coke-bottle spectacles, once again demonstrates here superior marksmenship by single handedly wiping out the entire enemy bomber squadron with antique deck gun".

The second part, was a Star Trek joke, based upon the scene where (IIRC Christopher Loyd, playing the Klingon commander), orders his gunner to aim for the federation ships engines, with the goal of capturing the ship. The gunner fires on the federation ship, but utterly destroys it, and exclaims (just before being shot by his commander) "Lucky shot, sir"!

Hence, while posting a thread about an alternate Germany, that takes a serious look at what they can realistically do to defeat the UK by building a purpose built "ship hunting" naval aviation force, and reading a response that seems to be implying that a lone British merchantman (even with 11 AA guns), is both going to shrug off the damage from a 5 plane attack, while at the same time infilcting serious losses upon such a force, well.:rolleyes:

Firstly this type of German/Nazi/Not-the-Nazis-but-do-as-well timeline dismisses any form of intelligent response from those ranged against your superior warrior race.
A couple things about this part of your post. First, where in the thread do I endorce Nazism? So where, therefore, do I deserve to get slandered by the bolded portion? Second, if you are offended by threads that posit a Germany that is not as badly run as OTL Nazi germany was run, without some form of 'better' French and UK counter, perhaps avoiding those threads (and then being offended all over again), might be a better way to go? IIUC, OTL Nazi Germany beating France was a fluke, not some stroke of genius on the part of Germany, as OTL they didn't have any plans nor forces ready to take the war to the UK.:eek:

Secondly, you ignore the likelihood of people reading your witticisms who actually know or knew and were related to those who fought in these campaigns.
This is a fair point, I feel, but I have to respond with an american bit of slang. I really had no idea that folks reading this thread would get "Bent out of shape" over my previous post.

Once again, I apologise for any offense given.
 
ATL instead of OTL doesn't mean that their aircraft are suddenly immune to 20mm cannon fire.

As for shipping routing - yes, they routed around the areas of greatest threat, meaning the eastern Atlantic around the French west coast.
True, but...

Would you care to compare my posited attack profile with the OTL attack profile? I think it might prove useful to have them both side by side, and then I can cover each point one by one.
 
As above, re-read post #12.

I'll wait for someone that actually has the physics, to explain that one.
Perhaps at this point, I should ask you to explain the attack profile as YOU envision it, because your posts don't seem to match what I posited as the attack profile.
Wait, you were actually serious about 40mm/.50 cals in turrets, and that the turret would only weight 2,000 lbs????? A 40mm Bofors (to get you the 2lb shell) weighs 1,000 lbs per gun, and a naval twin mounting gets you another 10-15,000 lbs, 2,000 lbs for another 500 rounds per gun. You're missing a zero there just for the mounting alone, let alone the reinforcement the airframe will require to cope with the recoil.
For comparison, one of the most heavily armed turrets built during the war was the Boulton Paul type H. That was armed with a pair of 20mm Hispanos, and allowing for 300 rounds per gun was 1,300 lbs including gunner.

So far as rounds penetrating the water goes, of course some of them will penetrate quite some distance. The problem is that they are very rapidly losing velocity, and depending on the angle a number will ricochet off the surface. Remember that the ships aren't made of paper-thin material like aircraft - 1" thick plates are not uncommon, not from any form of armour but simply because they need the structural strength to stay together.

Finally, your attack profile seems explicitly designed to do several things, none of them good:
  1. Ensure the guns are installed in the heaviest possible manner, minimising range and payload.
  2. Maximising the amount of time your aircraft stays over the target, ensuring that any gunners have plenty of time left to shoot at it. Note also that you are presenting a broadside on target to any AA gunners.
  3. Making your gunner's aiming job hard, by ensuring that he is always firing deflection shots against a target at a continually changing angle. That obviates any chance you have to get decent concentration of fire against a single spot.
  4. Ensuring you're in trouble if bounced by fighters - bombs and torpedoes can be jettisoned at need, a turret cannot be.
 
The artic convoys were beefed up with AAA and the guns were manned not by "my Grampa" but by men like his brother (my Great Uncle) who was seconded from 5th AA Division who completed his war landing with the 11th Armoured (D+7 Epsom, Goodwood, Bluecoat, Market Garden and liberating Bergen-Belsen)
I find your assertion quite insulting on two levels:-
Firstly this type of German/Nazi/Not-the-Nazis-but-do-as-well timeline dismisses any form of intelligent response from those ranged against your superior warrior race.
Secondly, you ignore the likelihood of people reading your witticisms who actually knew or knew and were related to those who fought in these campaigns


Actually, at least on the tanker my father was on, the AA guns were manned by the crew. He still has the certificate they gave him for completing the necessary gunnery course.

The army crews were mainly for the 4" guns, I believe the AA was sometime army, sometimes, crew, sometimes a mix. It varied from ship to ship.
 
Ugh, I regret participating in the cf of a thread now.

Bro, hanging around firing 50cals and 40mms from a whizbang turret in a medium bomber is perhaps the second least effective method of sinking a merchant vessel I've heard of. First being level bombing from 20,000ft.

First off, they aren't going to let in significant amounts of water because hits under the waterline will be rare. Second, even the US B25s with 75mms and a battery of 50 did not rely on the guns alone to sink merchants. Third you won't find many confined watertight compartments in a merchant, they will be large open areas such as a cargo hold, or an engine room, and a couple ounces of HE won't produce significant overpressure.

The OTL Germans actually had an effective counter shipping doctrine with torpedo carrying HE111s and JU88s. The second best counter-shipping attack to torpedos is skip bombing. The problem will be getting medium bombers to the merchants, since most of them will be outside the range of the medium bombers.
 
The real problem with this scenario is that the planes you propose simply don't have the range to get to the convoys with any sort of war load (including guns, 40mm rounds are heavy)

As this is all planned before WW2, you cant aim to fly over France, Britain or the Channel. You have to assume the Admiralty isn't drinking lead paint, and would send their convoys on the southern route. So you have to fly up the North Sea, around Scotland, and then a considerable distance to the convoy routes. Then FIND a convoy. I wonder where Germany is finding all the fuel for this 4-engined fleet...?

Given WW2 tech, this needs a 4 engine heavy bomber equivalent. Which are horribly expensive. And we are assuming that the British don't decide to put some long-range fighters (with drop tanks) in Scotland or the Orkneys to make your trip home a little more exciting...:p

There is a rather large difference between a huge torpedo hole and lots of small holes. The torpedo lets in a lot more water, much faster. It causes an immediate list, and often damages the ships keep. Small holes are easier to manage (and btw, a typical torpedo hit would open a hole around 170,000 times the size of a 40mm round...)
 
It's the submarine. Preferably long-ranged and with a lot of working torpedoes. If it has high submerged speed and a schnorckel, so much the better.
 
Other then torpedos, skip bombing.

Small calibers guns aren't really effective at sinking large ships, they make lots of holes up top, but they don't make large holes to let water in.
Actually I think air dropped naval mines might actually be the most effective way for planes to sink merchantmen, during the last six months of the war they sank more tonnage than every other source IIRC
 

takerma

Banned
Canons are not going to do it. If you gonna have a plane like that with internal bomb bay. Load torpedoes in there. Ditch the turret and all extra weight. Your best defence is range and size of the ocean. It will be a some time till escort carriers are a problem.

How good were German air launched torpedoes anyway?

If written realistically and not as wank this could be a fascinating tactical study. Once escort carrier become available in number though it will start getting a bit one sided.
 
Actually I think air dropped naval mines might actually be the most effective way for planes to sink merchantmen, during the last six months of the war they sank more tonnage than every other source IIRC

Dont think its going to work very well against an enemy that has coatal radar an airforce and lots of minesweepers
 
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