"Tom Anderson" wrote

It seems strange that they wanted to keep the route in tunnel all the way
to Gunnersbury; the current track layout means you can surface at Turnham
Green and go from there (via Chiswick Park, ish) without getting in
anyone's way. Maybe it wasn't always like that, or they thought a stop at
the Green itself was more useful.

The situation in 1920 was that the District had been electrified by 1905 to
Wimbledon, Richmond, Hounslow Barracks (later renamed West), Ealing
Broadway, and South Harrow. This used the LSWR between Hammersmith (Studland
Road Junction) and Turnham Green, though this section had been quadrupled in
1905, with the District having sole use of the southern electrified pair.
The LSWR service, which used the northern pair, ran from Addison Road (now
Olympia) via Hammersmith Grove Road to Richmond, and was withdrawn in 1916,
leaving this pair of lines derelict (but still in the ownership of the
LSWR).

This meant that the District was congested west of Earls Court, so the
proposal to extend the Central Line to Richmond would have provided relief.
In the event, the LSWR service was never reinstated. In 1932 tracks between
Hammersmith and Turnham Green were rearranged, quadrupling was extended to
Northfields, and the Piccadilly was extended to take over the Hounslow and
South Harrow (extended to Rayners Lane and over the Met to Uxbridge) lines.
Even then, Studland Road Junction to Turnham Green remained in SR ownership,
leased to the District (as part of the Underground group, soon to be
absorbed into the London Passenger Transport Board).

Peter