On Bundesarchiv RM 7/2386 there's a memo of 6 May 1940 about adapting the He 111 and Ju 88 for torpedo operations
This note starts off:
1) Available Aircraft
There are three He 111 H at E-Stelle Travemünde with special fittings for the use of torpedoes. These are not series aircraft but prototypes (V.28, 29 30?). On these three aircraft the series installation for torpedoes has been carried out. They can carry two torpedoes and have the requisite adjustment devices for torpedoes.
The question mark is in the original text but does anyone know anything more about the V28, V29 and V30, e.g. their Werk Nummern?
(Annoyingly, the memo's second page, about the Ju 88, is missing by the way).