MAC was initially set up in response to the flooding of the Afon Tryweryn valley and the village of Capel Celyn to provide water for Liverpool.
On 10 February 1963 a transformer at the dam construction site was blown up by three men, of whom one, Emyr Llywelyn Jones, was identified, convicted and sentenced to one year imprisonment.
On 30 June 1969, the evening before the investiture, two members of MAC, Alwyn Jones and George Taylor, were killed when a bomb they had been placing near government offices exploded prematurely.
[1] The final bomb was placed on Llandudno Pier and was designed to stop the Royal Yacht Britannia from docking - this too failed to explode.
In an interview shown on the BBC2 4 July 2009, John Jenkins repeated his intention that the bombs were never planted or timed to hurt people but just to disrupt the ceremony.