The keel laying, which marks the start of construction and assembly, was marked with a ceremony attended by Britain's Minister for Defense Equipment, Support and Technology Philip Dunne and coincided with an announcement that the first two submarines of the class are nearing completion of sea trials.
"The keel laying of the sixth submarine, Agamemnon, and the handover of HMS Astute and HMS Ambush to the Royal Navy are huge milestones reflecting significant progress in the program," Dunne said.
"This is the sixth submarine in the Astute Class and we expect her to be built more quickly and efficiently than her predecessors, demonstrating the effectiveness of the national submarine building capability in Barrow-in-Furness (the location of the BAE shipyard).
The seven Astute Class submarines have greater firepower, enhanced communications equipment and advanced stealth technology. They are replacing the Royal Navy's Trafalgar class submarines.
BAE Systems Maritime Submarines is responsible for delivering all seven Astute Class submarines.