Geography plays its part. Fortunately!
It is interesting to follow the course of the U-boat war via the merchant ship sinkings month by month. How from 1939 it spread westwards into the Atlantic as bases in France became available, then times like Operation Drumbeat, then the move to South African waters etc.
The U-boat War in World War Two (Kriegsmarine, 1939-1945) and World War One (Kaiserliche Marine, 1914-1918) and the Allied efforts to counter the threat. This section includes over 21.000 Allied Warships and over 11.000 Allied Commanders of WWII, from the US Navy, Royal Navy, Royal Canadian...
uboat.net
Operation Drumbeat sent U-boats across the Atlantic to operate off the US and Caribbean coasts in early 1942. A distance of 3,600-4,500 miles. This was a journey that was within the capabilties of the not just the long range Type IX U-boats but also the Type VII U-boats which formed the bulk of the U-boat fleet in WW2 (over 700 completions).
MId-1942 did see the Kriegsmarine tackling shipping traffic in the Central Atlantic and around Freetown. Freetown was the big convoy terminus in the region. Ships stopped to rebunker and re-store. It was here they joined convoys to sail north or convoys broke up to allow ships to sail independently either south or across to the South American coast. At least one of the big southbound WS troop convoys took a 300 mile diversion out into the Atlantic in autumn 1942 after leaving Freetown to avoid an area of U-boat activity.
Bordeaux (the southernmost U-boat base in France) to Cape Town is 5,800 miles while to Durban on the IO side it is 6,600 miles. The vast majority of the U-boats sent to the IO area were the long range Type IX (a couple of Type X boats and 2 Type VIIF torpedo transports were also despatched). At the outbreak of WW2 only about 7 of the 56 U-boats in service were of that type. Total completions of various models of that Type only reached 193 by the time the last one commissioned in May 1944. The range of these began at 10,500 miles and was gradually increased to c13,500 miles in the Type IXC (141 completed from 1941) to 23,700 miles in the Type IXD (30 completed from early 1942). So allowing for losses, refits, work up times etc as well as the long journey times there were never huge numbers available to send to the South Atlantic & IO.
Britain became very concerned about the Axis setting up a submarine base on Madagascar following the Japanese occupation of southern French Indochina at the end of July 1941. Not necessarily by a Japanese invasion but also by Vichy French acquiessence in allowing either Japan or Germany use of harbour facilities such as existed at Diego Suarez. By Nov 1941 Britain was planning the invasion of Madagascar. That plan was temporarily put on the back burner after Pearl Harbor only to be resurrected in early 1942 and carried out from May to Nov 1942 starting with Operation Ironclad. It would however have taken a lot of resource to set up such a base and then to defend it.
Britain set up an extensive system of bases on the various island chains in the IO to allow active hunting for both surface raiders and submarines, both German & Japanese. So from the Indian coast up near Calcutta, down through Madras, Ceylon, the Maldives (Addu Atoll), Diego Garcia (Chagos Archipeligo), Mauritius, Seychelles to Madagascar (after May 1942) to the South African coast then up through Dar es Salaam (Tanganika), Zanzibar, Mombasa (Kenya, home to the Eastern Fleet from mid-1942 to the end of 1943) to Massawa & Port Sudan on the Red Sea. Then across the Arabian Sea to places like Khormaksar (Yemen), Masirah (an island off Oman), Bombay on the west coast of India.The work to do that began before the outbreak of war with Japan and evolved to the end of 1944.
By Sept 1942 there were for example 4 Catalina squadrons operating across the region. By June 1943 it was 6 squadrons. And more General Recce aircraft continued to arrive into 1944. These squadrons would send detachments from their home bases to patrol the vast expanse of ocean as required. And as I noted in my last post the escort carrier Battler entered the arena in Oct 1943 followed by others in 1944 until the threat had reduced so far that they could be deployed on other duties in 1945.
As well as the shipping traffic to Egypt and India there was also the increasing Lend Lease deliveries from late 1942 to the Persian Gulf. Eventually something like nearly 25% of supplies to the USSR went via that route.
The problem got worse for the Germans after the Med was reopened to through traffic from May 1943 and it was once again able to use the Suez Canal. The amount of traffic routing via the Cape to the MIddle East & India reduced significantly and was then mostly in the northern Indian Ocean / Arabian Sea Area. Meanwhile the German subs couldn't make use of the Suez Canal and actually had an even longer journey to make. That is when a U-boat base at Penang really came into its own. It has just dawned on me how Monsun dovetails with the reopening of the Med. You can see the change in pattern by comparing the locations of the monthly sinkings.
The Japanese anti-shipping campaign in 1942 was unusual for them, as they saw attacking enemy fleets as the main target of their subs.
So while it may seem like a strategic mistake, it was one that Donitz could really do little about in the early war years. Too few Type IX U-boats early on. The opportunity to use a base in the DEI didn't arise until mid-1942, and by mid-1943 much of the opportunity had evaporated to a large extent with the re-opening of the Med. Once a decision was taken to open a Far East U-boat base the problem was then one of keeping it supplied with torpedoes & other technical eqpt. Pretty much everything except oil still had to come from Germany. For torpedoes the Type VIIF U-boat would have been a big help but only 4 were built.
