The British E class submarines started out as improved versions of the British D class submarine. All of the first group and some of the second group were completed before the outbreak of World War I. The group 1 boats of the E class cost £101,900 per hull but the price eventually increased when the second group entered service to £105,700 per hull. As submarine technology improved, the E class went through several modifications to install the new improvements which were all installed by the time the final group was under construction.