More details emerge about plan to replace Royal Navy Harpoon anti-ship missile

This week the MoD Weapons, Torpedoes, Tomahawk and Harpoon (TTH) Project Team issued a Contract Notice (CN) which outlines more of the requirements for a new weapon to replace the Harpoon Block 1C anti-ship missiles.

In March 2019 the MoD issued a Prior Information Notice (PIN), not a formal request for tender but a document that sets out their general requirements to potential contractors. This provided reassurance the obsolete Harpoon 1C would actually be replaced by an interim purchase. Until 2017 the RN had accepted that budget pressures meant Harpoon would go out of service in 2020 with no replacement. The retirement date was pushed back to 2023 and now funding has been secured to replace the system, at least on a modest scale.

The PIN states the available budget would be up to £200M, enough to buy a stock of missiles, logistic and training support until the FCASW is available in the early 2030s. (The Future Cruise and Anti-Ship Weapon is an Anglo-French project to replace a variety of long-range missiles with new generation technology, it is unclear, as yet if it will be capable of hypersonic speeds or another subsonic stealthy cruise missile). As a critical bi-lateral international project, it is important to signal to the French that I-SSGW will only be a small purchase to cover a 10-year capability gap and does not mean the UK is losing interest in FCASW.

The contract notice, issued on 19th August says the Interim Surface to Surface Guided Weapon (I-SSGW) is to provide “a ship-launched, over-the-horizon precision anti-ship capability and a terrain-following precision maritime land attack capability.” The desire for land-attack capability is sound and but adds another dimension to the project. Although the deterrence factor of having the ability to sink other ships is critical, recent history suggests we are much more likely to need to hit inland targets than attack shipping. The RN’s limited stock of Tomahawk Land Attack Missiles (TLAM) can only be fired from submarines. On a good day, the RN is able to put only 2 or 3 SSNs to sea and they have a multitude of other pressing tasks. The RN’s land-attack capability has been used in several conflicts and is a powerful tool but may require the SSN to loiter in suitable firing area for some time. Frigates able to attack land targets offers greater flexibility and an alternative, if less stealthy, option. Many modern AShM feature land-attack modes already so this would be a big gain for little extra cost.

It should be noted that TLAM is more powerful than the AShM hybrids and has a 1,000lb warhead and a range of about 900nm. The RAF’s Storm Shadow has a 450kg warhead optimised for bunker-busting so I-SSGW would complete a suite of UK land-attack weapons, each with its own advantages.

Mind the gap. It appears the four Type 45 destroyers currently fitted with Harpoon will revert to empty decks forward of the bridge when Harpoon is retired. (The space forward of the Sea Viper silo and behind the 4.5″ gun is designed to accommodate 16 x Mk41 VLS cells and all the goodies that would offer).

To keep the good news in perspective, the CN states that the MoD only expects to equip just 5 towed array Type 23 frigates with the I-SSGW and their main role would be “protection of a Maritime Task Group”. It is likely the missiles would be shared around the frigates as they deploy. To accommodate the new weapon on the Type 23, they will have to be canister-launched and have the same approximate footprint of the Harpoons they replace. Although essentially a bolt-on system in needs to interface with the combat management system and the ship or other platforms may need to exchange data with the missile in flight.

Saab RBS15 Mk 3 AShM canisters being loaded onto a Polish warship (Photo: Saab)

Given that the I-SSGW must be fitted to Type 23 frigates (without massive modifications) and have terrain-following land attack capability, the possible candidates are being narrowed down to three likely options. All three of these potential candidates are subsonic, optimised for use in cluttered littoral environments, can follow complex attack profiles, use stealthy composite materials and are resistant to electronic countermeasures.


The Lockheed Martin Long Range Anti-Ship Missile (LRASM) AGM-158C is the largest, most capable but expensive option, thought to be around $4M per missile. It has a range of over 200nm and a 1,000lb warhead. LM have demonstrated a canister-launched vision but it will be launched from Mk 41 VLS cells or aircraft by the USN, its only confirmed customer so far.


Developed in Norway, the Kongsberg Naval Strike Missile (NSM) has about 100 nm range and a small 125Kg warhead. At 410 lbs total weight it is the smallest of the options by some margin. Although more accurate, it has about half the hitting power of the Harpoon it might replace. It has been in service since 2012 and successfully exported to several navies, notably bought by the USN for its Littoral Combat Ships.

RBS15 Mk 4

The latest version of the Saab RBS15 Mk 4 ‘Gungnir’ (Odin’s Spear) looks closest to hitting the RN’s ‘sweet spot’ for price, size and punch. Although the RBS15 can trace its heritage back to the 1980s, the Gungnir is a completely refreshed design that only came on the market in 2018 and will be in service with the Swedish navy by mid-2020. It has as a range of about 160nm and a 200kg warhead. (The CGI at the top of the article shows the Gungnir being fired from a shipboard canister in a littoral environment. The two boosters fall away soon after launch).

The MoD wants the first shipboard equipment for I-SSGW installed by December 2022 with delivery of missiles following a year later. The contract with the weapon supplier would be for at least 4 years, probably extended for a further 9 years. This would include manufacture, delivery and installation as well as training, maintenance and technical support. The towed array type 23 frigates are scheduled to leave service between 2028 and 2035 which would fit with a total 13-year contract. It also is possible that the I-SSGW could also eventually be fitted to the Type 31e frigates.

It is encouraging to see the RN will acquire a modern anti-ship missile and land-attack capability to a defined timetable and budget. Stocks are likely to be small and really represents a bare-minimum for a fleet of the Royal Navy’s stature and ambition.