The 5ft 6in Tank was a 2-4-2T locomotive designed by Webb for fast passenger service. In general, it was a tank version of Webb's Precursor class. The wheels actually had a diameter of 5 feet and 8½ inches with tires and the 5 feet and 6 inches from the class designation only stood for the diameter of the wheel centres. The cylinders were 17 inches in diameter and 24 inches in stroke and were controlled by Allan valve gear.

The LNWR built 160 between 1890 and 1897 in their Crewe shops. When the LNWR became part of the LMS in 1923, only three had been withdrawn. They were now assigned to power class 1P and between 1929 and 1932, 42 were fitted for working push-pull trains. Two were sold to the War Department in 1930 and 1931. When British Railways were founded in 1948, only 43 were remaining. The last ones were withdrawn in 1955 and none were preserved.