Type XV and XVI - large transport and repair U-boats

my scenario would be for ships built on Admiral Hipper-class, they would need a tanker for extended operations and helpful if they could launch and/or retrieve seaplanes. (think the high pressure steam, at the time, was a reasonable gamble)

(btw that is good idea for towed tank, similar or same design schemed to carry V-2?)


That was part of that original proposal as mentioned in Rossler THE-UBoat..pp 207 []along with Kohr's transport U-boat proposal]., to use off the shelf technology.
 
The Dithmarschen were ammo and repair ships in addition to fuel. They could also make over 21 knots. Without aircraft facilities you could pass for a tanker and not attract as much attention.Late war design IJN oilers had facilities to launch replacement aircraft for carriers.

Some form of air patrol would be an advantage. Perhaps light cruisers on the hybrid Swedish Gotland type rather than the K Class.

Yes as were the civilian tankers trailed in the Spanish civil war. That would be part of the notion of redirecting the effort to civilian tankers and then repurpose the Dithmarschen builds as PBC. It is of note that post war this was the lesson they gleaned from these vessels, to build them to warship standards with fleet speeds as the Dithmarschen were.

KM did have a handful of Helicopters trailed throughout the war- that could assist in scouting for underway replenishment. I think Operation Berlin was the only time the Dithmarschen tankers accompanied the warships. All other vessels and replenishment missions were conducted through disguised remote linkup.
 
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The so-called 'Flak Traps' were ordered by Donitz. U-Boats (and indeed all early submarines) travel primarily on the surface where they are faster. They only dive to attack or avoid attack. U-Boat losses in the Bay of Biscay were becoming alarming due to the surfaced U-Boats being attacked by Allied aircraft. Thus the 'Flak Traps' were created with single (or even twin) 37mm and quad 20mm AA guns plus extra single 15mm heavy AAMG's and 20mm cannons. Their skippers had orders to fight it out with Allied aircraft in the hopes this would convince the Allies to leave all surfaced U-Boats alone.

It didn't work and losses remained heavy. Donitz finally called it quits and had the 'Flak Traps' converted back to normal AA (usually a single 37mm plus a twin 20mm).

The U-Flaks were no less vulnerable to the HVAR and 60lb rockets American and British planes started carrying as well
 
The U-Flaks were no less vulnerable to the HVAR and 60lb rockets American and British planes started carrying as well

There simply were too many Allied aircraft hunting subs by this time for any single sub, no matter how much AA it carried, to fight off. And new weapons like rockets, retro-rocket DC's and the 'Leigh Light' were coming into service which made them even more dangerous.
 
There simply were too many Allied aircraft hunting subs by this time for any single sub, no matter how much AA it carried, to fight off. And new weapons like rockets, retro-rocket DC's and the 'Leigh Light' were coming into service which made them even more dangerous.

Yes the solution was the U-Boat schnorkel, it would eliminate over 1/2 of the historical U-Boat kills. Dr Walther devised in 1933 a schnorkel for his experimental U boat . Walthers schnorkel was ponderous, but could maintain ~ 25 knots submerged through his super peroxide drive system and dealt with the over pressurization issue. They did have the simple Dutch design which was in theory available for adaption after 1940 and Walther did developed the historic KM system starting after a proposal to Donitz in Feb 1943. Within 6 months they had model ready for trials, but it would take until late 43 before for contracts to be issued and early 44 before installed on new boats.

At anytime this schnorkel idea could have been ordered and put into service within a year. As far back as 1938 both Furbringer and Kleikamp stressed the need for options in the upcoming U-Boat war. Donitz was right about the offensive impact of the Wolf Pact tactics, but in large part because LW was no where to be seen. Furbringer stressed the strength of U-Boats was their invisibility when submerged- but also warned Donitz that it was only a matter of time before allied ASW was to drive the Wolf Pacts underwater; destroying any offensive effectiveness. Integrated LW support to find and attack Convoys. Kleikamp also reiterated the need for integrated LW support and stressed the danger in wolf pact radio communications being intercepted -only accelerating this crises. Donitz ignored all this since only coordination of sweeping Wolf-pacts had any chance of finding convoys at sea.
 
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SwampTiger

Banned
I doubt any of these solutions would be of use if production starts after 1941. The British were getting the upper hand. The Germans were less prepared than the Dutch in the East Indies. At least they had a coordinated strategy using subs and MPA's.

A rather cumbersome solution to the Supply and Maintenance U-Boat would be a docking well built into the hull capable of holding a U-boat larger than the Type IX. Sort an undersea LSD able to hold a U-boat under replenishment, with some sort of overhead crane system for loading torpedoes and heavy supply crates. I doubt the technology was available to seal the docking area if submerged. Expense would equal a BB.
 
Greenland is looking better and better as a resupply option?
There are plenty of ‘off shipping routes’ too. The oceans a big place.
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