[9] With the outbreak of the Second World War, he returned to ordnance work as a civilian government scientist, defusing German bombs around the United Kingdom, under the cover occupation of an inspector of air raid shelters.
When it did detonate, it caused minimal damage and for his actions he was awarded the George Cross on 3 December 1940.
Merriman's George Cross citation appeared in the London Gazette on 3 December 1940:[2] The King has been graciously pleased to approve the award of the George Cross to:- Arthur Douglas Merriman, Part-time Experimental Officer, Directorate of Scientific Research, Ministry of Supply.
[12] On 6 January 1944 he was named an Officer of the Order of the British Empire for "gallant and distinguished services in the Middle East".
[15] On 27 June 2013 The Daily Telegraph reported that Merriman's George Cross had been put up for auction by his nephew, with an estimate of £60,000.