The Mk 54 Torpedo is so far the only weapon that has been cleared for use on the aircraft in British service.
The information came to light from the response to a written parliamentary question:
Kevan Jones, MP for North Durham, asked:
“To ask the Secretary of State for Defence, what armaments are the UK P-8 permitted to carry as of 4 January 2022.”
Jeremy Quin, Minister for Defence Procurement, responded:
“As at 4 January 2022 the Poseidon MRA1 has been cleared for Anti-Submarine Warfare, Anti-Surface Warfare and Search and Rescue in support of submarines. It is assisted in these roles by its sophisticated suite of radar and data gathering equipment. The Mk 54 Torpedo has been cleared for use on the aircraft.”
Currently, no British weapon has been cleared for usage on the aircraft but it’s hoped that will change in future.
Back in 2018, a $40 million contract was awarded for the production of MK54 Mod 0 lightweight torpedo kits for the US, UK, Canada, Australia and Taiwan.
“Progeny Systems has been awarded a $40,601,413 cost-plus-fixed-fee, cost-plus-incentive-fee, fixed-price-incentive-fee contract for the production of MK54 Mod 1 lightweight torpedo kits and related test equipment, spares, and engineering and hardware support services.”
Back in 2016, then Minister for Defence Procurement Philip Dunne said:
“The Department intends to bring the P-8A into service without significant modification to ensure the delivery of operational capability as soon as is practicable. There are no current plans to integrate Stormshadow or other UK manufactured weapons onto the aircraft.”
The P-8 itself is able to conduct anti-submarine warfare, anti-surface warfare and shipping interdiction along with an electronic signals intelligence role. Undertaking this roles would require the aircraft (in British service as the Americans already do this) to be cleared to carrying various missiles and other weapons. It is able to drop and monitor sonobuoys.