The Huntly rail bridge bombing occurred on the Glen Afton (or Awaroa) Branch, near Huntly, New Zealand around 3 AM on 30 April 1951, when high explosives were set off on a railway bridge. The bombing took place amid the 1951 New Zealand waterfront dispute, an industrial dispute over the working conditions and wages of dockworkers. Characterised by the-then Prime Minister Sidney Holland as an act of terrorism, the bombing caused no casualties, even though a morning passenger train ran over the weakened bridge. The perpetrators remain unknown. Waikato coalfields Coal was first mined from the Waikato coalfields west of Huntly in 1849. By 1951, both pit (underground) and open-cast (surface) mining techniques were being used. Trade unions Depending on the mine and mining techniques used, the 1500 Waikato miners were members of either the larger national United Mineworkers' Union, who worked the pit mines, or the smaller local Northern Miners' Union who worked some of the open-cast mines. Small disputes during 1950 had revealed different attitudes both between and within the union memberships. 1951 waterfront dispute On 13 February 1951, the national executive of the New Zealand Waterside Workers’ Union decided its members would only work a 40-hour week, and imposed an overtime ban. In response, the employers stood the men down until the following Saturday. By 21 February, the Government had passed emergency regulations and declared a state of national emergency. By 27 February, most of the Waikato miners were on strike, in support of the watersiders, and members of various unions refusing to work brought mining at most Waikato mines to a standstill. Coal shortage By the start of March 1951, Waikato dairy companies dependent on local coal were reporting they had a week to ten days supply left. Initially, the Auckland Gas Company expected it would be able to maintain gas supplies. Yet by 12 March, the company said it could only maintain gas supplies for 3 meal periods a day for 17 days after receiving a fresh shipment of coal, while half the retort house workers were dismissed after they refused duty and walked out. Even though the Waikato open-cast miners returned to work at the beginning of April 1951, this came too late for the freighter Lochybank, which had been in Auckland port since 18 February, and had to load 150 tons of firewood instead of unobtainable bunker coal so that it could sail