The Re 456 were originally known as Re 4/4 KTU (Konzessionierte Transport-Unternehmungen) according to Wikipedia.
If I remember correctly, BT ordered 6 and SZU ordered 2. A later follow up order for an additional 4 from the SZU also saw VHB order 2 of this class.
The BT Loks were rebranded when the BT merged with the SOB in 2002. They were soon joined by the pair of former VHB Loks, which were leased from the BLS after it acquired the RM (EBT/VHB/SMB) and determined that it did not need those two Loks. The former RM Loks were used primarily for freight and coach transfer operations, as they were not equipped for operation with the SOB's pendelzug coaches.
As was stated, the Re 4/4 KTU served as the prototype for the SBB Re 450 Series. It also played a key role in the development of narrow gauge Loks of the Rhaetische Bahn and the MOB (Ge 4/4III)
I would like to know more about what exactly KTU meant. Did it only apply to the Re 4/4 (456)?
I know that in the case of the BDe 4/4, those were known as the EAV Triebwagen (Eidgenössischen Amt für Verkehr).
Was KTU a grouping put together specifically for the Re 4/4 purchase or did it function in other aspects/acquisitions as well?
From what I recall, I don't remember running into KTU associated with any other locomotives or rolling stock.