He remained there until World War I when Filon was called to active service and Jeffrey became head of the Applied Mathematics Department. However as a Quaker he became a conscientious objector.
Siya ay nanatili doon hanggang sa World War ko kapag Filon ay tinatawag na aktibo sa serbisyo at Jeffrey ay naging pinuno ng Applied Mathematics Department. Subalit bilang isang Kweiker siya ay naging isang matapat objector.