Best airborne anti shipping weapon?

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In the RAF/Coastal Command, weapon use went through a cycle.

Initially, medium altitude level bombing was the preferred method, being seen as the best compromise between accuracy and survivability. In addition, early UK aerial torpedoes had some problems with break-up and off angle running..
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hen the limitations of bombing accuracy against moving sea targets and the effectiveness of flak at medium altitude was realised, attacks moved towards low level torpedo bombing (late 1940 onwards). This was in combination with the entry of remedies to some of the limitations of torpedoes and the increasing deployment of the Beaufort as a torpedo bomber. The Beaufort was also a notably poor level bombing platform, which might have also prompted the tactical shift.

From around March/April 1943 RP-3s began to replace torps. A combination of the two weapons was seen as the best choice, with Beauforts, Beaufighters and occasionally Mosquitos providing a mixed force providing both flak supression and destructive power. Later the combination of rocket armed Beaufighters and Mossies worked very well for the Coastal Command anti-ship patrols around Norway.

In mid-late 1943, the Beufort also began to be used for shallow angle dive bombing attacks by the RAF and also RAAF. This was mostly employed against merchantmen, as this was considered somewhat suicidal against warships. In the Med in 1943, UK anti-ship ops would have included bombers, torp carriers and rocket carriers.

The RAAF also used the Beauforts for level bombing attacks, after changes to the engine nacels, wing leading edges, dorsal turret and increasing the tail area by 15% increased directional stability and made for a better bombing platform.

The 6lbr Molins, for all that it gets talked about, wasn't actually used that much, with only 18 Tse Tse Mosquitos being build and maybe only 15 seeing active service.
 
Part of the change in weapons was also due to the change in targets. By 1943 the Germans didn't have that many "torpedo worthy" ships left. A lot of coastal shipping and/or their escorts are small and hard to hit with a torpedo. Or are running in shallow water.

The use of mixed armament (bombs, torpedos and rockets) indicates no one weapon was the "cure-all". Against larger ships (and warships) the rockets provided AA suppression and would sink the smaller ones the torpedoes had trouble hitting. The torpedoes could sink the larger ships that could absorb multiple rocket hits without sinking. Bombs tended to work on most ships that didn't have several inches of armor.
 
In what terms?

They could be very effective if all went according to plan, See damage to HMS Belfast.

However they cannot be used in open oceans/seaways. about useless in a Pacific carrier battle.

They can be "swept", which called for dropping them at night so they are not spotted.

They can tie up lots of resources countering them and prevent ship sailings for days delaying transport and tying up shipping even without sinking anything. German mines took a lot of "countering" around England in 1940/41.

Mines dropped by B-29s against the Japanese had a tremendous impact on shutting down Japanese supply/transport at the end of WW II.
 
My objective was to explore how resources devoted to air dropped mines compared to resources devoted to other airborne anti shipping weapons. Certainly very useful in the restricted waters of the North Sea. Gardening sorties were always at risk from Bomber Command strategic bombing thinking which is why the Royal Navy wanted Coastal Command to be subject to their control. The RAF had no place controlling maritime resources.

Like artillery, mines are an area denial weapon whose deployment can be more significant than the damage actually inflicted. On the Western Front in WW1 artillery was the queen of the battlefield being able to seal off any incursions through the front lines until a counter attack could take place.

Coastal sea traffic was far more important then than now. Britain continued to sail coastal convoys through the Dover Straits and along the East coast despite air, mine and torpedo boat attacks as the road and rail systems simply could not move enough things across the country. The German Atlantic Wall was built using coastal transport delivered cement, sand, gravel, shuttering and steel.
 

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Oldcrow, those tonnages seem ambitious. Just reading from the Graphs , and not including "naval" I count well over 10m tons of japanese shipping sunk. they never had 10 million tons of shipping to sink
 
Oldcrow, those tonnages seem ambitious. Just reading from the Graphs , and not including "naval" I count well over 10m tons of japanese shipping sunk. they never had 10 million tons of shipping to sink

Now that you mention it, it does seem quite high. I believe (from such impeccable sources as wikipedia) that Nazi U-boats sank 14.5 million tons. The same source says the USN destroyed over 5 million tons of IJ shipping. However, it looks like that tonnage is the combined total of Naval and merchant shipping so the graph is indeed inaccurate and overestimates the losses by a fairly substantial amount (>>10%). It looks like the total japanese merchant losses from all sources was something closer to ~8.5 million tons.

Here is another source of tonnage breakdown including contributions from allied forces.

Japanese Naval and Merchant Shipping Losses During World War II by All Causes
 
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I dont thjink that is correct, concerning allied losses. according to HMSO returns, the losses to allied controlled shipping 1939-45, by year were (in 000's tons):

1939: 755
1940: 3992
1941: 4329
1942; 7997
1943: 2002 (Jan to May)
1943: 1219 (Jul to dec)
1944: 515 (Jan to May)
1944: 531 (Jun to Dec)
1945: 439 (to august)

685 or 14.5 million tons were due to enemy submarines, (with close to 2 million tons sunk by japanese submarines in the pacific and Indian oceans), followed, in descending order, by a/c, mines, warship, merchant raider, eboats, and accident.
 
I dont thjink that is correct, concerning allied losses. according to HMSO returns, the losses to allied controlled shipping 1939-45, by year were (in 000's tons):

1939: 755
1940: 3992
1941: 4329
1942; 7997
1943: 2002 (Jan to May)
1943: 1219 (Jul to dec)
1944: 515 (Jan to May)
1944: 531 (Jun to Dec)
1945: 439 (to august)

685 or 14.5 million tons were due to enemy submarines, (with close to 2 million tons sunk by japanese submarines in the pacific and Indian oceans), followed, in descending order, by a/c, mines, warship, merchant raider, eboats, and accident.

I believe the allied losses I quoted were due to KM Subs only. I did not attempt to discover the losses to IJN subs which were substantial with regard to USN warships. It seems to me, IJN subs were more effective in the significance of their target and timing than in the gross tonnage they sank. Sinking the damaged Yorktown, Juneau and undamaged Wasp, the double tap of the Saratoga, and nonfatal hits on battleships. Their hits were timely and if perhaps not sinking their targets outright, removed them from service during critical periods of the war. Otherwise, the quantitatively incorrect graph above seems to indicate a prioritization pretty much as you've listed: subs, a/c, mines, etc.
 
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Ive got an excellent book on the operations by IJN subs. Their anti-shipping efforts were patchy, and not a 100% effort like the German efforts. Japanese doctrine called for their subs to attrition USN battleships prior to the the decisive battle in the central pacfic. They were designed with a top surface speed of 24 knots, so that they could attack the advancing US battlewagaons (21 knot behemoths) and then circle back for another attack(s) as this fleet advanced. That theory was wrecked by the advent of the fast batteships and carriers, which simply, and mostly just left the Japanese subs behind as they steamed to targets. Of course, there was the unforeseen increase in detection and attack capabilities of the USN light forces. Later, much effort was wasted on frivolous issues like re-supply of beleagured garrsions and nuisance raids and the like. But it is also completely untrue to claim that IJN IBoats were not alive to tonnage warfare, or were not used for that purpose. Quite successful (if rather minor) campaigns were conducted on the east coast of Australi and in the Indian Oceans for example. The tonnage campaign between Hawaii and the west coast was however, spectacuallrly unsuccessful, which is where I suspect the myth that their subs were not used to sink merchant ships might have arisen
 
I've always found the IJN submarines especially interesting. AFAIK, the IJN pioneered the effective use of long-range, aircraft carrier subs.

One tangentially related thing I've read recently, is that USN asw ops typically constrained the speed of their escorted units to below 15 knots because they 'incorrectly' believed they could more effectively protect their merchant or fleet charges. According to the story, USN ASW was NOT effective at such speeds and Wasp and Sara suffered the consequences. I'd love to know the speed constraints on RN destroyer SONAR. I would expect that to be the ASW high water standard.
 
Thanks FM, if the site is correct, the RN system had a fair edge on the USN equipment. I believe the USN advertised 13 knots as effective speed with 15 as a max for its SONAR, while your site stated:

"Maximum design speed for the dome was 25 knots but on Haida, the maximum working speed was 20 knots. When retracting or extending the dome, it was necessary to check the voltage of the mains supply. In a 220 volt mains' system, the voltage could not drop below 180 volts. If it did, the contactor in the control board could fail to operate thus causing the dome to bump against the end stops and cause damage."

I assume the higher speed was for dome stuctural purposes and the lower was ASDIC operating speed. 20 knots might have preserved CV Wasp, DD O'Brien and prevented damage to BB NC.
 
Ive got an excellent book on the operations by IJN subs. ..snip....
May I ask which book? I only have "The Japanese Submarine Force and World War II" by Boyd and Yoshida. I once borrowed a copy of "Submarines of the Imperial Japanese Navy" by Carpenter Polmar, which might be the best on designs and specifications. I have never read "Sunk: The Story of the Japanese Submarine Fleet, 1941-1945" by Hashimoto and Beach.

The IJN submarines may have been ineffective because they could not find targets in the Pacific especially if they were confronted with patrolling aircraft. Aircraft were a very serious problem for Japanese submarines because they were the slowest to submerge. For example, shutting down the Diesels and engaging the electric motors required more than pulling one lever or even a few levers (Boyd and Yoshida, page 42). I think that Americans were faster and German and British submarines were quicker still. The Mozambique Channel and off Australia may have been the only places where the IJN submarines could find weakly escorted enemy merchant ships.

For comparison, German submarines had the best hydrophones of WW2, they used the wolf pack tactics and they sometimes had information from broken Allied codes. British submarines in the Mediterranean had a much smaller area to search and were also helped by code breaking. American submarines had the best radar of WW2 and information from code breaking. They even had an ability to search better when surfaced by raising their periscope high above the sail (is that name anachronistic?).
 
Japanese subs were large and vulnerable, but they did posses some advantages as well. They were long legged and fast, at least on the surface. Some carried seaplanes, which may have offset their lack of radar, and given them some reasonable search capabilities in the wide spaces of the pacific.

With regards to success, the Japanese enjoyed success on the east Coast and in the Mozambique channel, as you say, But this success spilled over into the Souythwest pacific (not quite the Eastern seaboard of Australia) as well as the Bay Of Bengal and the Indian Ocean generally. at the beginning of the war their submarines were very successful in the Far East. They had virtually no success off the US west coast and hawaii, in tems of merchant shipping sunk.

Japan simply didnt have enough subs, and many of those that they did have were poorly used insofar as they were wedded to a doctrine already obsolete by the time war broke out. According to Yoshida and Boyd later in the war many subs were used for transport, where many were lost and for no real gain
 

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