BAC,

In answer to question 2:

i) The type XXI and type XXIII were much more advanced than the other U-Boat types and needed completely different tactics and operating procedures to be employed. These new methods of U-Boat war took time to perfect and it took time to train crews on these new methods. When you remember that an 'ordinary' type VII or type IX could take over a year to reach the 'front' after being commissioned the new U-Boats took alot longer to 'work-up'. With the first Type XXI's being commissioned in mid 1944 it would be mid 1945 at the earliest before any of them would be ready for frontline service.

ii) The allies extensively mined the baltic which constantly delayed the training schedule of the Type XXI and XXIII.

iii) A combination of the allies Strategic bombing campaign and scarce materials meant that many of the new type XXI's and XXIII's were actually un-fit for service due to cronic defects in their hulls and machinery.Clay Blair is paticularly diss-missive of the type XXI's bulid quality and points out that the boats actually had
fundamental design flaws which would have rendered them allmost useless in service. (the Schnorkel did not work properly,the Hydraulic system was dangerous and the hull was too weak..some hull rings had been cut away to support equipment and the design office was not informed...this took quite a bit off the diving depth).

iv) Diesel fuel was not in as short supply as petrol during the last months of the war but it was more scarce than it had been.The problem was that the quality of deisel deteriorated as the war went on and this affected the reliability of the diesel engines..they wore out quicker and they broke down more often.

I hope this answers your question

Rgrds

Sniper.