The London Treaty allowed for an escalation clause that would allow the construction of battleships of 45,000 tons and carrying 16" guns. With Germany, Japan, and the Soviet Union reported to be building 60,000 ton battleships it was felt that a class of battleships in the 40,000 ton range would suffice.
The Lion class would be similar in layout to the King George V class in design and would use improved 16" guns and turrets than the Nelson class. Triple turrets were also selected to simplify production. The 16" Mk II guns could fire a 2,375 lb shell 40,560 yards at an elevation of 40°.
The 1938 Program authorized two ships to be built and were ordered on January 21, 1939. In the 1939 Program two more were authorized and one was ordered on August 16, 1939.
It was decided with other more urgent needs for construction the class was cancelled.