Most were scrapped between 1921 and 1926 but "K26" survived until 1931, then being broken up because her displacement exceeded the limits for submarine displacement in the London Naval Treaty of 1930. "K18", "K19" and "K20" became the new M-class submarines. "K21", "K23", "K24", "K25", "K27" and "K28" were cancelled. Although the concept of a submarine fast enough to operate with a battle fleet eventually fell out of favour, it was still an important consideration in the design of the in the late 1920s.