As the business flourished and grew, Armstrong became an important employer on Tyneside. He took his responsibilities as an employer seriously and concerned himself with the welfare of his workers, founding a Literary and Mechanics Institute for them as well as a school. However, workers at Elswick joined with workers from other factories in the Nine Hours' Strike in 1871, campaigning for a shorter working day. In common with other employers, Armstrong took a firm stance against the striking workers, and was viewed by many as being a cold, remote figure who was out of touch with his workers.
In a pamphlet published by the Nine Hours' Movement, which details the dialogue between the employers, represented by Armstrong, and their workers during the strike, some of Armstrong's letters to the workers are reprinted in full. In one such letter, Armstrong wrote:
"However desirable a reduction in the hours of labour may be, the decision of the question must rest on commercial, and not sentimental considerations." 11