….because the Spitfire's elliptical wing was intended to allow (relatively) high Mach numbers
No it wasn't ! High speed (in terms of dynamic pressure as opposed to Mach number) was because the wing had a low thickness/chord ratio.
Elliptical lift distribution offers constant downwash across the span and hence low induced drag.
BEagle is correct
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...with RTR (redacted thrust reheat)
I know not where you found that strange terminology. The Jaguar had part-throttle reheat (PTR) whereby afterburner would remain lit when the engine was throttled back as far as about 90% rpm. It was selectable by switches just below the canopy rails on the left hand side.
I have 1850 hours on the aeroplane.