After
much debate in Parliament the contract to build the tunnels was won by John
Mowlem and Company. February 1915 saw the commencement of the construction of
the tunnels from a series of shafts dug at points along the route of the line.
Most of the line was constructed in London Clay, using the Greathead shield
system, hand mining was used for the connecting tunnels at stations.
Due to the outbreak of World War 1, work on the railways electrical
systems was suspended, but for safety reasons, work on the tunnels was allowed
to continue until completed. During 1917, due to the shortage of labour and
materials, Mowlem had to suspend work on the stations. During the later years
of the war the tunnels were used to house some of the Capitals art collection,
from the Tate Gallery, National Portrait Gallery, British Museum and the
Wallace Collection.
Just out of interest, the stations were used as dormitories for Post Office
staff during the Second World War. It was not until June 1924 that track
laying was commenced using 1000 tons of running rail and 160 tons of conductor
rail. 1925 
saw
the commencement of the installation of the electrical equipment, lifts,
conveyors and mail chutes. Again progress was
slowed, this time by the General Strike and the electrical installation took a
lot longer than expected. It was not until February 1927 that the first
section, between Paddington and West Central District Office, was available
for training. October 1927 saw the finishing touches put to the railway, and
the line was available for use for the Christmas parcel post. February 1928
saw the first letter post on the system.
It was decided in 1954, that
because of the problems of access at the Western District Office, Wimpole Street
and the Western Central District Office, New Oxford Street that a new Western
District Office would be built at Rathbone Place. This entailed building a
diversion to the line that would run through the basement of the new office. The
trains were diverted onto the new line in 1958. It was not until 3 August 1965
that the new station and office was opened by the then, Postmaster General,
Anthony Wedgwood-Ben. The
disused section was used as a store tunnel, some parts of it still have the track
in place.
The main line consisted of a
single tube, 9 foot in diameter. The base of the tube was f
illed
with loose ballast, on which a concrete raft, 12 inchs thick was laid. Onto this
was laid the track. The tunnels diverge using a step-plate junction just before
the stations, into 2 single line tunnels at 7 foot in diameter. These then
connect to 2 parallel station tunnels, which are around 25 foot in diameter. The
platforms are built on a 'First floor level' within the tunnels, the area
beneath, used to house the electrical control equipment.
Although the main tube is at a
depth of around 70 foot, the stations are constructed at a much shallower depth,
giving a 1 in 20 rise and fall, into and out of the station. This served two purposes, the first is that the mail
had
less distance to travel from the platforms to the surface. Secondly the gradient
on the line, to and from the station, served to help slow the trains on their
approach to the stations, and assists with the acceleration away from the
stations.
