Document ID: chunk:federal_register_of_legislation:F2022L00620:body:0:p32
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accommodate a Typex cypher machine, used for coding and decoding cables (Figure 23).  The Typex machine enabled Prime Minister John Curtin to communicate directly with British Prime Minister Winston Churchill and American President Franklin Roosevelt.  It was accommodated in a freestanding structure because of the highly sensitive nature of the cables.  In 1944, a metal staircase was added to the rear (east) elevation of West Block, to enable direct transfer of cables between the two buildings (Figure 24).
In 1945, no longer required to accommodate secret cables or provide shelter during an air attack, the former air raid shelter was adapted for use as an electrical substation in 1945, a use that it still serves.
Figure 19 Proposed temporary building for the Cables Branch (unbuilt), 1943
Source: National Archives of Australia, NAA CT86/1 474A
Figure 20 'D Block', pictured 1954, as viewed from the south-east
Source: National Archives of Australia, NAA A1200 11207749
Figure 21 Proposed additional office accommodation and new main entrance, West Block, 1945
Source: National Archives of Australia, NAA A2617, Section 14/16260
Figure 22 New main entrance to West Block in 1959, showing the original signage 'Commonwealth Office West Block'
Source: National Archives of Australia, NAA A1200, L32282
Figure 23 Ventilation and heating was installed at the 'Dugout' in 1943, for the adaptation of the air raid shelter to accommodate a Typex decoding machine
Source: National Archives of Australia (Department of the Interior, Works Branch, 30 December 1942, M7439C)
Figure 24 East elevation of B Block, 1944: an external staircase provided access into the building from the Dugout
Source: National Archives of Australia, NAA A2617 Section 14/15165

2.6.2               Alterations and additions, 1940-46
              1940-41 Pneumatic tube installed linking the Secretariat buildings and Parliament House
              c.1942 An air raid shelter was constructed to the east of West Block.  The building was adapted in 1943 for use as a secure communications facility
              1944 D Block was constructed at the south end of the building in the same architectural style as the original building
              1945 Conversion of air raid shelter to electrical substation
              1945 Open courtyard enclosed on east side of B Block and automatic telephone exchange installed
              1946 Open courtyard enclosed on west side of B Block, creating a new entrance to the building. New cruciform lobby created at centre of B Block
Floor plans illustrating the incremental development of West Block are at Figure 26, Figure 27, Figure 28 and Figure 29.

2.7                    Post-World War II 1946-60s
After the end of the war, the building was still undergoing expansion.  Despite the creation of additional office space in the enclosing of the courtyards in B Block, the building required further expansion.  The major change was extensions made to A Block