By Jed Cawthorne

01.  Introduction
02.  Overview of the Arrowhead 140 design
03.  The need for more guns
04.  Italian style and flair
05.  Summary



Babcock Type 31e Light Frigate Proposal (Image: Babcock International)

01.  Introduction

With the cost of of Type 26 ASW Frigates and Type 45 AAW Destroyers running to up to £750 million or £1 billion per ship, the total number of vessels that can be afforded by the Royal Navy has been reduced. Since no ship can be in two places at the same time, there comes a point where absolute ship numbers cannot be reduced beyond a certain level. That number appears to be 19 surface combatants. With six Type 45 Destroyers and eight Type 26 Frigates, there was a need for a low-cost general purpose frigate. This requirement will be filled by the Type 31e Light Frigate (no one use the word Corvette).

Over the past two years, the Royal Navy has evaluated three bids from Bae Systems / Camell Laird, Babcock and Atlas Elektronic UK. In September 2019, at the DSEI Defence exhibition, the Government announced that the Babcock Arrowhead 140 designhad been chosen as the RN’s preferred Type 31e Light Frigate option. Following-on from this, there has been much conjecture about how this new class of ships will be equipped, including the combat management systems, sensors and weapons. An excellent analysis of this can be found at:

There is some concern that the proposed weapon fit will not deliver sufficient firepower for the roles envisaged, especially when new threats, such as drone swarms, fast attack craft and hypersonic missiles are considered. Therefore, this article will look at the proposed weapons and consider whether better options exist. This discussion does not limit itself to Type 31e and some of the weapons currently under consideration for this warship could well be used across the fleet.

Babcock model of its Type 31e Light Frigate proposal showing different weapon fit options. (Image: Nicholas Drummond)

02.  Overview of the Arrowhead 140 design 

The Type 31e Frigate is intended to provide the Navy with an inexpensive general purpose warship with the range and endurance needed for global maritime security operations. It must be able to operate alongside Type 45 Destroyers, which are specialist anti-air warfare ships, and with the new T26 Frigates 3(or Global Combat Ship) which are specialist anti-submarine warfare ships. The Babcock Arrowhead 140 design is based on the Danish OMT design bureau’s design for the Danish Navy’s Iver Huitfeld-Class of AAW Frigates 4, which in turn is based on the earlier Absalon-Class multi-role support ship.

The Arrowhead 140 displaces 5,700 tonnes, measures 138m in length, is 20m wide and has a crew of potentially less than 100, but accommodation for 180. With a proven hull, it is notably larger than other vessel designs submitted for the competition.  In contrast, my first ship, HMS Hermione (F58) which I joined in 1984, was a Batch 3 Sea Wolf Leander-Class Frigate.She was the last RN ship to be refitted in Chatham Naval Dockyard and also served as a general purpose light frigate. She displaced 3,300 tonnes (fully loaded), measured 112m in length and was 13m wide. The steam-powered Leanders required a crew of 250. She was armed with the Sea Wolf GSW25 point defence missile system, 4 x Exocet anti-ship missiles, 5 x 20mm cannon, 2 x triple torpedo tubes, and a Lynx helicopter with Stingray torpedoes or Sea Skua anti-ship missiles.

As the difference in displacements shows, the modern Type 31e GP frigate will be much larger, offering better sea-keeping abilities, greater range and endurance, and more modern, comfortable living conditions for her crew. Four reconfigurable boat bays plus additional crew accommodation mean that RN boat crews or RM boarding parties will be able to provide excellent maritime security capabilities, supported by either a Wildcat or Merlin helicopter. A bank of 24 Sea Ceptor / CAMM surface-to-air missile cells amidships will provide cutting-edge short-range anti-missile / anti-aircraft capabilities. The new vessel is also expected have a hull-mounted sonar that is at least equivalent to that of Type 45 Destroyer and the ability to embark a Merlin Mk2 ASW helicopter, to provide baseline ASW capabilities. These could be enhanced by adding Unmanned Surface Vessels for ASW in place of some boats and potentially a containerised towed array sonar in the deck mission space below and behind the flight deck, which will be able to carry multiple 20-ft ISO containers. Additionally, the RN has issued an RFP for a new ‘Interim Anti-Ship Missile’ to replace the obsolete Harpoon used on the five existing Type 23 GP Frigates.

The main search radar will likely be the Thales NS110 AESA radar or possibly the newer NS200 GaN AESA set. With detection ranges of 110 miles or more, these systems are comparable in performance, but lower in cost than the similar BAE Artisan system used on Type 23, the QE carriers and Type 26. Decoys are likely to be the standard RN DLF floating radar decoys and Sea Gnat Chaff/IR flare mortar system, lifted from decommissioned Type 23s.

Ultimately, the size and flexibility of the Type 31e vessel means they can be expected to have a meaningful role within a carrier task group, even if their main role is to deploy globally on maritime security operations, allowing Type 45 Destroyers and Type 26 Frigates to focus on Carrier Strike Group operations. The low cost and modularity of the design also means the ship could have significant export potential.


03.  The need for more guns

After the DSEI announcement, details started to emerge of the proposed weapon fit for Type 31e. While no official details have yet been released, the following weapons are expected to be fitted:

  • Main gun – 57 mm Bae Systems / Bofors Mk 3 / Mk. 110 gun8 with rapid fire capability and a 10.6 mile / 17 km range
  • Secondary gun – 40 mm Bae Systems / Bofors Mk. 4 gun9with the ability to engage air and surface targets, making it ideal for neutralising fast attack craft and with a range of 12 miles / 19.2 km
  • Air defence – 24-cell Sea Ceptor / CAMM VLS
  • Point defence- 2 x 30 mm SCG / ASCG cannons7 mounted aft
  • Point defence – 2 x 7.62 mm miniguns mounted forward
  • Decoy system – 2 x Sea Gnat decoy launchers (From Type 23)
  • Space for Anti-ship Missile canisters – TBC
  • Miscellaneous weapons – 2 x 7.62 mm GP machine guns

Assuming the above configuration is correct, the choice of weapons may not provide sufficient firepower in all situations, making the Type 31e a larger version of a lightly-armed OPV (albeit one with a SAM capability).

Bae Systems / Bofors 57 mm Mk 3 / Mk 110 gun (Image: Bae Systems)

As the ‘Save The Royal Navy’ article notes, the 57 mm Bofors and 40 mm Bofors both make sense if the T31 has to counter small boat swarms, attacks by suicide boats, helicopters, light aircraft, or even drones. It also states that fitting the BAe 127mm / 5-inch gun,10 which will be mounted on the Type 26 Frigate, is considered to be too expensive for Type 31e. With the Type 45 AAW Destroyer continuing to use the ubiquitous 4.5-inch gun, the multi-role, but ASW focused Type 26 will adopt a NATO-standard 127 mm / 5-inch gun, acquiring a third type of smaller gun for  Type 31 seems short-sighted.

Fitting a 127 mm gun is perfectly valid for a Type 26 ASW Frigate, giving it flexibility and lethality across a range of situations, its primary role will be ASW, so it would be expected to use its main gun less than a Type 31e will, especially as Type 26 also has VLS launch tubes for anti-ship missiles such as Tomahawk or whatever replaces Harpoon. In case the capabilities of a 127 mm gun are required, the Navy would need to detach a Type 26  for use in littoral waters and give it a Naval Gunnery Support (NGS) mission on the ‘gun line’ – which is actually where Type 31e should come in. In other words, the 127 mm gun is more appropriate for Type 31e than it is for Type 26.


Bofors 40mm mk4
Bae Systems / Bofors 40 mm Mk 4 gun (Image: Bae Systems)

Introducing the Bofors 40mmto the RN adds greater range while offering more a more flexible range of ammunition than the current 30mm Mk44 Bushmaster in its MSI Seahawk 12lightweight remote mount. The BAe FUZE 3P programmable fuse with pre-fragmented rounds for both the 40mm and 57mm guns gives them excellent anti-small boat swarm performance, and even an anti-missile capability. Despite a lower rate of fire, HE proximity fuse rounds can throw an impressive cloud of shrapnel at an incoming missile at double the range of a stream of 20mm projectiles from a Phalanx CIWS.14 Thus, adding the Bofors 40mm gun to the inventory and supply system makes sense if it is to be used widely to replace the Phalanx in various vessels. I am no fan of the Phalanx, it was introduced to the RN at the same time as I was, in the early 80s, and I have had two different careers since, so hope to see it retired in favour of a more modern and capable system. As good as the Bofors 40 mm is, there are better alternatives, including the latest modifications to remote 30mm mounts that add five Martlet laser-guided lightweight multi-role missiles (LMM).12There is also the Thales RapidFire,15a turret mounted 40mm CTA cannon with air burst ammunition (although Thales suggests that a 200 rpm gun is not really an anti-missile system).

General Dynamics Phalanx 20 mm CIWS (Image: Naval Today)

Perhaps though, the best alternative to the Bofors 40mm, for a fleet wide fit, would be its big brother, the 57 mm Mk3, widely deployed in the US Navy as the Mk110 gun. The turret has a non-deck penetrating mount and weighs 7 tonnes . It is capable of 220 rounds per minute out to 17 km against surface targets. As noted above, it can use the same advanced fuse system as the 40mm, providing an air-burst capability against air and surface targets, as well as impact detonation, or delayed action against bigger surface or land targets. Even more interesting is the BAe ORKA16advanced ammunition. The ‘Ordnance for Rapid Kill of Attack craft’ is a 57mm guided round with anti-surface and anti-air capabilities. These are provided by an imaging seeker that can also lock-on to an illuminated laser reflection. Beyond ORKA is DARPA’s MAD-FIRES, a 57mm gun launched point-defence anti-missile missile. Details about this can be found on this video:


DS30 Remote Automatic Cannon – MSI Seahawk mount with Bushmaster Mk44 gun and 5 x Thales Martlet (LMM) missiles.(Image: Jed Cawthorne)

With ORKA and 3P ammunition, a turret with a hoist, with an ammo handling system for 1,000 rounds (for applications where deck penetration is not a problem), and weight of 14 tonnes, this is an extremely flexible weapons system. A magazine-fed system in B and Z positions on the T31 would provide a fantastic anti-swarm capability. As we are unlikley ever to send one of only six highly specialised (and costly) Type 45 AAW Destroyers to provide NGS missions, it might make sense to remove the 4.5 inch Mk 8 from use and replace it with a 57mm Mk. 3, plus replace Phalanx with non-deck penetrating 57mm turrets.

Apparently, there were some comments at DSEI about improving the lethality of the Batch 2 River Class OPV’s – replacing their forward 30mm mount with a non-deck penetrating 57mm Mk3 mount would provide a considerable uplift in capability for these vessels.

04.  Italian style and flair

The Bofors 57mm is not the only game in town. Many of our European Naval allies use the Leonardo / OTO-Melara 76mm Super Rapid gun.6  With an even greater range than the 57mm gun, it has similar advanced fused ammunition types, giving it a multi-role capability as well as using standard HE ammunition.17It has an interesting sub-calibre round called the DART, which is radar guided as part of the STRALES system, providing a guided anti-missile capability.18The standard air-burst HE rounds are useful for dealing with small boat swarms, but a 76mm version of the Vulcano 19provides extended-range unguided and guided capabilities against larger enemy ships and surface targets. OTO-Melara’s scaled-down version of their 127mm projectile,20which we could fire using our BAe Mk45 127mm / 5-inch guns. The Italian Navy mounts multiple Super Rapid guns on its Frigates and Destroyers in the CIWS anti-missile role. German, Dutch, Danish and Spanish navies all use older versions of the same 76mm light gun.

Leonardo / OTO-Melara 76 mm Super Rapid gun (Image: OTO-Melara)

05.  Summary

Advanced electronics applied to ammunition fuses, advanced materials used for lightweight mounts with ballistic protection, advanced barrel designs that offer improved ranges and automatic ammunition handling systems that offer higher rates of fire are driving a renaissance in naval gunnery, from 30mm up to 127mm. These advances can improve the self-defence and offensive capabilities for RN ships, from River class OPV’s to the QE class carriers.

As the Type 23s are eventually replaced by the Type 26 with its 127mm gun, and by the Type 31e, we should seize the opportunity to remove the venerable and ubiquitous 4.5 inch from service. We could replace the 4.5-inch gun on the Type 45 with a 127mm, but do we really need to? The Type 31e, however, as a General Purpose Frigate, that does not perform specialist deep water AAW or ASW roles, should really be a candidate for a 127mm main gun, giving it littoral combat and NGS capabilities for its ‘high end conflict’ role within the overall fleet.

The Bofors 57mm has the flexibility to replace the Phalanx CIWS on the Type 45 Destroyer and Queen Elizabeth-Class Carriers and potentially on some RFAs too. While the 57mm is no doubt more expensive than the Bofors 40mm, I question the cost of introducing a third new mount with the attendant training, maintenance, supply chain and ammunition supply burdens. In some respects a 30mm DS30 mount with five Martlet missiles has an advantage over the 40mm, while the 57mm has range and ORKA in its favour. So if we could afford it, it would be good to see the future fleet equipped as follows:

Type 45 AAW Destroyer

  • 57mm with magazine in A mount replacing 4.5 inch gun
  • 57mm non-deck penetrating mounts port and starboard to replace Phalanx
  • Port and starboard DS30 remote mounts with Martlet

Type 26 ASW Frigate

  • 127mm Mk45 in A mount
  • 57mm port and starboard non-deck penetrating mounts instead of Phalanx
  • Port and starboard hanger roof DS30 remote mounts with Martlet

Type 31 GP Light Frigate 

  • 127mm Mk45 in A mount
  • 57mm deck penetrating with magazine in B (in front of bridge) and Z (central hanger roof) positions
  • Port and starboard hanger roof DS30 remote mounts with Martlet

River Batch 3 Offshore Patrol Vessel

  • 57mm non-deck penetrating mount in A position
  • Port and starboard DS30 with Martlet abaft of boat davits

In conclusion, this mix of weapons amounts to a lot of 57mm gun turrets, but there is much to be said for standardisation and commonality of spares, training and ammunition. This would give each major surface unit five gun mounts, with a mix of 127mm, 57mm and 30mm. A bit better than the 5 x 20mm manually aimed guns of my first ship, and better than the 4.5 inch, 2 x Phalanx and 2 x 20mm of my final ship, the T42 Destroyer HMS Glasgow.




  1. Babcock Arrowhead 140 Site –
  2. org – More details on the T31 –
  3. BAe Systems Global Combat Ship (RN Type 26) –
  4. Danish Iver Huitfeld Class –
  5. Leander Sea Wolf / Exocet conversion –,_Seawolf/Exocet_conversion
  6. Leonardo OTO Super Rapid 76mm light weight naval gun –
  7. DS30BM 30mm Remote mount with Bushmaster M44 30mm cannon –
  8. BAe Mk110 / Bofors 57 Mk 57mm system –
  9. BAe Bofors 40 Mk4 Naval gun – 40mm cannon –
  10. Bae Mk45 Mod 4 127mm Naval Gun –
  11. 5 Inch / 114mm Mk 8 Gun –
  12. DS30BM mount with Martlet (Light-weight Multi-role Missile) –
  13. Fuze 3P – 57mm multi-purpose ammunition –
  14. Phalanx 1B 20mm CIWS –
  15. Thales RapidFire 40mm CTA turret –
  16. BAE 57mm ORKA –
  17. Leonardo 4AP programmable fuze for 76mm and 127mm ammunition –
  18. DART guided sub-calibre projective for 76mm SR gun –
  19. OTO Vulcano 76mm extended range / guided munition –
  20. OTO Vulcano 127mm extended range / guided muntion –