Statistics

[CapnScurvy]

From a web site called "The Monsun U-Boats-WW2 German Submarines in Asia" I gleaned there were a total of 41 German U-Boats assigned to the Indian Ocean/Asia Theater.

32 were Attack U-Boats
7 Transport Subs / Fuelers
2 were gifts to the IJN

72 Ships were sunk, for a total of 426,000 GTR (Gross Register Tonnage)
16 U-Boats sunk at least one ship.
6 of the 16 successfully returned to Europe, the other 10 were sunk, or surrendered.

Of the remaining 25 U-Boats assigned to Asia without a kill:
17 were sunk en route.
3 sunk while on patrol, or making delivery.
1 aborted mission, returning to France.
4 surrendered at wars end

At any one time, only a handful of U-Boats were ever stationed in the Indian Ocean/Asia Theater