After the New Zealand Government declared war on Germany it decided to establish the New Zealand Expeditionary Force (NZEF) for overseas service. As a part of this force, the Wellington Mounted Rifles Regiment was formed and began concentrating at Awapuni racecourse in Palmerston North from 12 August 1914. Hastings joined the unit in the Manawatu and was attested on 13 August 1914, enlisting into the 6th Squadron as second-in-command under Major Charles Dick. The unit formed part of the New Zealand Mounted Rifles Brigade commanded by Brigadier-General Andrew Hamilton Russell, and departed New Zealand on board the troopship "Tahiti" on 15 October 1914. This vessel was one of twelve troop ships that carried the main body of the New Zealand Expeditionary Force in a convoy escorted by Allied warships. After departing New Zealand, the convoy stopped at Hobart, Albany and Colombo before arriving at the Suez Canal on 1 December 1914. In Egypt, the New Zealand Expeditionary Force established a training camp at Zeitoun, with the New Zealand Mounted Rifles Brigade remaining behind as the New Zealand Infantry Brigade participated in British operations against the Ottomans in the Suez Canal area in February 1915, before taking part in the invasion of the Gallipoli Peninsula in late April 1915.