The 680 tonne Forward Island, the seat of command for HMS Prince of Wales, contains the bridge and around 100 vital mission systems and compartments.
It also has deck-to-deck windows up to 6ft 6in (2m) tall, creating a level of visibility beyond that on previous aircraft carriers and designed to withstand powerful impacts, such as a helicopter’s spinning rotor blade.
The Aircraft Carrier Alliance began construction work on the structure at Govan in December 2013.
The block, which will eventually sit on top of the flight deck, was towed by barge from the Clyde on April 24 and made its way around the south coast of the UK before being delivered to Rosyth dockyard in Fife today for the next stage of assembly.
HMS Prince of Wales is the second Queen Elizabeth Class aircraft carrier being built for the Royal Navy.
Its sister ship, HMS Queen Elizabeth was the first to begin construction and could have jets flying off it by the end of 2018.
Those behind the project, which is estimated to cost more than £6 billion overall, say the QE Class will be the centrepiece of Britain’s naval capability.
Each 65,000 tonne aircraft carrier will provide the armed forces with a four acre military operating base which can be deployed worldwide.
The vessels are designed to be versatile enough to support war efforts or provide humanitarian aid and disaster relief.