In September, when Australian offensive activity was almost entirely moved underground, an ambitious project was put forward by Major General J.G. Legge, commanding the 2nd Australian Division, which echoed that discussed by Swinton and Norton Griffiths in France. Two deep-level galleries, wide enough for troops to move through two abreast, were to be driven beneath the Turkish rear trenches to emerge in the rear of the Nek position. The chief engineer of the Division opposed the scheme, but it was approved by Birdwood on 21 September. The work was carried out under Captain Harry Arnall, a Cornish-born New South Wales miner, with a party of miners from the infantry, and special efforts were made to keep it secret. When, in early December, Arnall’s tunnels approached the Turkish lines, the engineers working on the 60ft deep-level mining system heard Arnall’s miners working below them. Not having been told of the scheme, they assumed it to be a Turkish mine and began tunnelling to meet it. Despite the secrecy of the project, knowledge of the scheme became current in the 2nd Division: ‘some critics, putting it down as a wild venture, gave the tunnel the nickname of “Arnall’s Folly” by which it was generally known.’²³

The tunnels were not complete before evacuation and it is not clear where or how the tunnel was intended to emerge behind the Turkish lines, or how the attackers would exit safely without being detected.