So far what i figure out
HDTW started in end 1950s as Lox/Kerosine engine for Luftwaffen Interceptor (for Saunders-Roe SR.53 ???)
After end of Interceptor program, MBB modified it to HydroLox and tested successful during 1960s.
In 1970s with chaos in ELDO program provoke by Britain, they look into alternative what became Europa III proposals.
Two of them used HDTW the Europa IIIB and IIID, last one use it in first and second stage.
Other contender A/C used Blue Streak hardware and were not selected like D and modular E proposal.
Europa IIIB was selected because the First stage was french build, but the engine made issue.
HDTW was consider too radical by European minister who decide in place of ELDO Management.
A compromise was made that MBB and SEP build variant of HDTW called H20 engine,
(in mean time NASA scared the hell out Rocketdyne with Patent on HDTW for Shuttle Main engine)
1972 there low cost proposal were Europa III use two smaller french hydrolox engine HM6 or HM7.
Also came Alternative German MAN Europa III ME that not use H20 in begin, and CNES Lanceur de 3e génération de substitution.
Now after 11 failed launch of Europa rocket ended this Programm in 1974.
Out ashes came Phoenix: Lanceur de 3e génération de substitution
it use similar approach as Europa III ME, it use first stage of Europa III and same hardware for second stage,
and third stage with simple hydrolox engine the HM7
This became Ariane 1
What happen to H20 and HDTW after this is unknown to me.
Rocketdyne took some Design feature from it for RS-25 engines.
