This article examines the circumstances in which the old ships and craft of the post-1945 Royal Navy's Amphibious Warfare Squadron were replaced by the new assault ships HMS Fearless and Intrepid. It analyses the impact on the requirement for amphibious forces of the change in emphasis in the late 1950s from major war contingencies to a new focus on mobile and flexible forces capable of responding to limited crises overseas. This called for a radically different type of capability than had been provided by the Amphibious Warfare Squadron and eventually resulted in a force built around two commando carriers, two new assault ships and six logistic landing ships. The article analyses alternative plans for the shape and size of the new amphibious force and examines the different design studies that resulted. It identifies a number of different ship types that were considered and demonstrates that the requirement to be able to land a joint all-arms force of up to a brigade group, supported by tanks and artillery, was key to the eventual decision to build Fearless and Intrepid and establishes the strategic rationale that underpinned the construction of these ships and demonstrates why they were built as amphibious transport docks in favour of the other design options.