displacing nearly 16,000 tonnes and equipped with Trident II missiles (armed with nuclear weapons) and heavyweight Spearfish torpedoes, to carry out Operation Relentless, the United Kingdom's Continuous At Sea Deterrent (CASD). The UK government has committed to replace these submarines with four new s, which will enter service in the "early 2030s" to maintain this capability. Fleet submarines (SSN) As of August 2022, six fleet submarines are in commission, one and five (one of which was still working up to operational status as of August 2022). Two more Astute-class fleet submarines are scheduled to enter service by the mid-2020s while the remaining Trafalgar-class boat will be withdrawn. The Trafalgar class displace approximately 5,300 tonnes when submerged and are armed with Tomahawk land-attack missiles and Spearfish torpedoes. The Astute class at 7,400 tonnes are much larger and carry a larger number of Tomahawk missiles and Spearfish torpedoes. was the latest Astute-class boat to be commissioned. Fleet Air Arm The Fleet Air Arm (FAA) is the branch of the Royal Navy responsible for the operation of naval aircraft, it can trace its roots back to 1912 and the formation of the Royal Flying Corps. The Fleet Air Arm currently operates the AW-101 Merlin HC4 (in support of 3 Commando Brigade) as the Commando Helicopter Force; the AW-159 Wildcat HM2; the AW101 Merlin HM2 in the anti-submarine role; and the F-35B Lightning II in the carrier strike role. Pilots designated for rotary wing service train under No. 1 Flying Training School (1 FTS) at RAF Shawbury. Royal Marines The Royal Marines are an amphibious, specialised light infantry force of commandos, capable of deploying at short notice in support of His Majesty's Government's military and diplomatic objectives overseas. The Royal Marines are organised into a highly mobile light infantry brigade (3 Commando Brigade) and 7 commando units including 1 Assault Group Royal Marines, 43 Commando Fleet Protection Group Royal Marines and a company strength commitment to the Special Forces Support Group. The Corps operates in all environments and climates, though particular expertise and training is spent on amphibious warfare, Arctic warfare, mountain warfare, expeditionary warfare and commitment to the UK's Rapid Reaction Force. The Royal Marines are also the primary source of personnel for the Special Boat Service (SBS), the Royal Navy's contribution to the United Kingdom Special Forces. The Corps includes the Royal Marines Band Service, the musical wing of the Royal Navy.