The policy of relying on volunteers had sharply reduced the capacity of heavy industry to produce the munitions needed for the war. Historian R. J. Q. Adams reports that 19% of the men in the iron and steel industry entered the Army, 22% of the miners, 20% in the engineering trades, 24% in the electrical industries, 16% among small arms craftsmen, and 24% of the men who had been engaged in making high explosives.[66] In response critical industries were prioritised over the army ("reserved occupations"), including munitions, food production and merchant shipping.[61]