The tunnels were built by council workers during 1941 soon after the attack on Pearl Harbour. The original drawings are lodged in the council archives, Auckland Library.
The wide tunnel width is about 4.5 meters wide (14ft 8in), 2.7 meters tall (9ft).
The narrow tunnels are about 2.06 meters wide (6ft 9in), 1.98 meters tall (6ft 9in).
The tunnels were filled and sealed during 1946. They were filled with clay bricks, dimensions 26 x 26 x 11cm. The main tunnel does not appear to have been filled all the way to the ceiling, rather to about 800mm from the top. Possibly the main tunnel is completely sealed at the air vents (speculation).
The total combined length of the wide tunnels is about 1100 meters. Total length of the narrow tunnels is about 3500 meters. This puts the total volume at around 27000 cubic meters. If all the tunnels were completely filled it would therefore take over 3.5 million bricks.
The signatures on the plans.