In focus – the Arrowhead 140 Type 31e frigate candidate

Derived from the Danish Navy’s Iver Huitfeldt class frigate, the Arrowhead 140 is the Babcock/Thales concept for the Type 31e frigate competition. Here we look at the Danish parent design and the Arrowhead proposal in detail.

Doing it differently in Denmark

The Absalon class Logistic support ships and the following Iver Huitfeldt class frigates were developed in Denmark based on the same hull form. They have attracted global attention for their distinctive approach to design and procurement which delivered three large and credible warships for a total of around $1Bn. Even within the US naval community, there are many advocates for ‘the Danish model’ as a way to get more ships for their money. For the Royal Navy’s cost-conscious Type 31e programme this seems like a perfect fit, although the Huitfeldt may appear to be considerably larger at 5,700 tonnes than the “light frigate” envisaged at the outset of the project.

In order to control costs the Absalon/Huitfeldts drew on lessons from commercial naval architecture practice, notably from Maersk, the largest container shipping company in the world. The design has been kept as simple as possible with long straight cable and piping runs wherever it can be achieved. Large items of equipment have pre-planned access routes through the vessel with soft patches (removable deck and bulkhead panels) which simplifies construction, makes maintenance and upgrades faster and cheaper, allowing the ships to spend more time at sea. This is not an entirely new concept for warships, but was taken to another level by the Danish designers.


The decision to go for a large hull form allows more space to ease on-site maintenance, for example, the engine room has space to meet the OEM requirements for access to the diesel engines, not typically the case on more cramped warships. To be ready for future upgrades, there is the capacity to double power generation and space has been left for additional cable and pipe runs to ensure inserting future technology is as painless as possible, minimising modification of the existing ship’s structure and services. For an average warship, through-life maintenance and upgrades can be up to 60% of the entire cost of ownership. Every effort was made to maximise ship availability while reducing running costs.

The Danish navy also continued to evolve its STANFLEX concept of interchangeable standard size containerised payload modules for Absalon/Huitfeldt. Their ‘flexible warship’ philosophy aims to decouple payloads from platforms and uses standard interfaces so a ship can be quickly reconfigured for different roles with a variety of weapon or equipment fits. Removable modules, maintained ashore instead of on board the ship, further increase operational availability. The Danish navy considers STANFLEX a success for its requirements but it has not been adopted to the same extent by other navies. Arrowhead 140 will not feature STANFLEX, although the fixed spaces allocated for weapons and sensors are designed to allow substantial equipment changes to be straightforward.

Their commercial ship design heritage had given rise to a myth that the Huitfeldt does not meet full warship survivability standards. This is not the case and the design meets NATO shock protection certification (STANAG 4142, 4137 and 4549), nuclear, biological and chemical protection (STANAG 4447) and vital area armour protection (STANAG 4569). The ships have also passed the Royal Navy’s stringent FOST assessments and sea riders with expertise in damage control say the Huitfeldt class fully meet their high standards.

  • The handsome HDMS Iver Huitfeldt arriving in Plymouth Sound while undergoing Sea Training with the Royal Navy (Photo: RFA Nostalgia)

  • Starboard side of HDMS Iver Huitfeldt (Photo: RFA Nostalgia)

  • HDMS Niels Juel seen off Norway participating in ASW Exercise Dynamic Mongoose 2018. (Photo: NATO Marcom)

  • A standard test for new warship classes – the Iver Huitfeldt being shock-tested. Commercial off the shelf (COTS) equipment has been used wherever possible but has to meet naval standards.

  • One of the spacious engine rooms housing two of the four MTU diesels with ease of access for maintenance.

  • Note the unusual engine room air conditioning plant (top left) to create a good working environment for maintainers.

  • Danish Airforce EH101 (Merlin) in the hangar of Iver Huitfeldt.

  • The central missile section has considerable capacity – up to 24 ESSM air defence missiles, 32 Mk 41 Strike-length VLS cells and up to 16 Harpoon anti-ship missiles. Note the distinctive outward-slanting funnels to direct hot gasses away from the Smart-L radar are not needed in the Arrowhead 140.

  • The bridge.

  • The operations room – still running Microsoft Windows XP on some systems when this was taken in 2012.

  • The Ship Control Centre where propulsion and auxiliary machinery is monitored and controlled.

The Huitfeldt has simple, robust CODAD propulsion. Four MTU diesels can be clutched in to drive the ship in different configurations. A single engine can propel the ship at 18 knots with an exceptional range of about 9,300nm. Two diesels can make about 25 knots and using all four engines the ship can reach 29.3 knots in less than 120 seconds. Controllable pitch propellers and a 900 kW bow thruster make the ship highly manoeuvrable in confined harbours. Her two main engine rooms are well separated with an engineers workshop in between for enhanced survivability. The large hull form of the Absalon / Huitfeldt is almost identical and well understood and is proven in heavy weather, safely able to launch and recover boats up to sea state 7. A more stable ship is a better weapons and helicopter platform and less tiring for its crew, a significant advantage over the other two Type 31e candidates.

Despite her size, the Huitfeldt has a small ship’s company, another big saving in through-life costs and an important consideration for the RN. In cruising state she can be manned by a duty watch as small as 12 people. The Arrowhead will have a complement of less than 100 but has comfortable berths for up to 180. Danish crew are accommodated in single, twin or 4-berth cabins and in true Scandinavian style, have a sauna in addition to a gym and generous messing spaces.

Child of Huitfeldt – Arrowhead 140

The Huitfeldt is designed primarily as an anti-air warfare and anti-surface platform and is fitted with some high-end sensors and weapons which will not (at least initially) feature on the Arrowhead. The Type 31e is a ‘general purpose’ maritime security-orientated frigate and will not have the ESSM and Mk41 cells of the Huitfeldt. Thales APAR (Active Phased Array) and SMART-L (Signaal Multibeam Acquisition Radar for Tracking, L band) are likely to be replaced by a single more affordable radar. 24 Sea Ceptor VLS cells are virtually certain to be fitted to Arrowhead but otherwise, the precise weapon/sensor fit has not been published by Babcock.

Babcock says the Arrowhead hull has not been substantially changed except in a few places to ensure it conforms to the latest revisions to the Naval Ship Code (ANEP-77) and Lloyd’s Register’s Naval Ship Rules. The centre section of the superstructure has been modified to provide two additional boat bays capable of carrying four of the RN’s heaviest (9.5 tonne) RIBs. There is space and structural strength to add bigger davits capable of deploying heavier loads in future. A mission bay below the flight deck has space for 4 TEU 20 containers which must be loaded through a removable hatch by dockside crane. Although not comparable to the mission bay handling arrangements for the Type 26, for Arrowhead it is envisaged UAVs would be housed in the hangar, USVs would be handled in the boat bay with small UUVs deployed from the USVs or manned boats. The containers below the flight deck could house unmanned mission command systems or the space used as austere troop accommodation. The flight deck is of sufficient size to land a Chinook and the hangar can comfortably house a Merlin helicopter.

Arrowhead features Babcock’s new iFrigate™ technology. This is a monitoring system that measures the performance of the equipment on board in real time and advises engineers on the ship and ashore about maintenance tasks and spares needed. iFrigate is a development of the Complex Asset Performance Analytics (CAPA) already being used on the Type 23 life extension programme and a prototype is already at sea on an RN vessel. (The BAES equivalent – System Information Exploitation (SIE) technology is fitted to the Type 45 destroyers).

  • (Top) The general arrangement of the Huitfeldt parent design and (bottom) the Arrowhead 140 derivative. The most profound differences are the reduced weapon/sensor fit and two extra boat bays of the Arrowhead.

  • 3 Type 31e frigates steam together – from the initial imagery set of Arrowhead 140 released in May 2018.

  • In the more developed demonstration model, in addition to a centreline gun mount, there are two phalanx CIWS which could be fitted, budget permitting, on either side of the bridge roof. Note also the small rotary wing UAV on the flight deck, just in front of the Merlin.

  • Arrowhead midsection. The 24 cell Sea Ceptor silo is visible with potential for more VLS cells to be fitted in front. The main gun shown on the initial visuals is the OTO Melara 76mm Super Rapid mounting which has good all round short-medium range performance and can be used for defence against missiles and aircraft. The fire-control radar mounted at the foot of the mast.

  • The Arrowhead has A & B positions for two guns up to medium calibre and could theoretically restore the RN ability to deliver a ‘broadside’. When faced with possible swarm attack, more guns maybe useful. The forward mount in this configuration appears to be the Bofors 57 mm Mk 3.

  • Thales APAR (Active Phased Array) multifunction Radar currently fitted to the Huitfeldt but is unlikely to be affordable for Arrowhead. The main gun in this configuration appears to be the 127mm/5″ Mk 45 mount that will also equip the Type 26 frigate.

The optional extras – FFBNW

To keep within the strict budget all the Type 31e candidates will have limited baseline equipment fits but of the 3 options, the Arrowhead has by far the greatest potential to be substantially upgraded. There are signs of growing political support for real increases in the defence budget. If we take an optimistic view that in a few years the RN could be in a position to improve the capability of platforms they have, if not order more new ships, then the available space and design philosophy of Arrowhead is a good starting point. The broad beam allows large radars to be mounted and the central section has space to add strike-length Mk 41 or Sylver VLS cells in addition to Sea Ceptor. Potentially Arrowhead could be evolved to be a high-end combatant and it should be noted HMDS Peter Willemoes participated in exercise Formidable Shield 2017 and used her radars to track Ballistic Missile targets.

The Huitfeldt/Arrowhead is described as ‘quiet hull’ design and the bow mounted sonar would have some utility up to about 12 knots. The Huitfeldts are not in the same ASW class as a Type 26 and most critically their engines and machinery are not raft-mounted to reduce sound and vibration radiated into the water. There is space to allow Arrowhead to have raft-mounted machinery but this would have to be specified by the customer at the outset of construction. There is plenty of space in the stern to fit a towed array, possibly the Thales CAPTAS 2 which is smaller and cheaper than the CAPTAS-4 / Type 2087 fitted to the Type 23/26. Alternatively achieving some Type 31e ASW capability, at least in the littorals, might be better served by investing in off-board systems such as UUVs or towed arrays deployed by USV. The aft section of the ship and mission bay could also be modified quite easily with a ramp to launch boats down a ramp off the stern.

The industrial angle

Although Babcock are the lead for the Arrowhead bid, the “Team 31” consortium includes other important contributors. Thales is a large defence multi-national that manufacturers sensors, communications and combat systems found on warships all over the world. They are one of the RN’s largest suppliers and have years of experience integrating systems in partnership with many other defence contractors. BMT Defence Services are another substantial company with particular expertise in naval architecture. Engineers from the original designers, OMT are also embedded in Team 31.

Team 31 say their Arrowhead construction strategy is in line with Sir John Parker’s National Shipbuilding strategy and a flexible, block build approach will include Ferguson Marine on the Clyde and Harland and Wolff in Belfast with assembly and integration done at Rosyth. At least 70% of the equipment for Arrowhead will come from UK suppliers. As partners in the Aircraft Carrier Alliance Babcock has residual on-site experience of major warship construction, although as the carrier project winds down there have already been some job losses. Many large sections, including 1,000-tonne sponsons for the QEC were manufactured at the site and the panel-line and fabrication facilities could easily be revived to work on Type 31e (and potentially, the Fleet Solid Support ship). The Huitfeldt/Arrowhead is designed to be constructed from 115 sub-units which are joined into 5 ’superblocks’ for assembly. For now, Babcock have secured the Goliath crane at Rosyth, critical for the movement of superblocks, which was put up for sale by the ACA in 2017.

The intellectual property rights (IPR) for the Huitfeldt design were licensed from naval architects OMT in Denmark and then developed further by Team 31 into Arrowhead. IPR for Arrowhead now resides entirely in the UK and can be exported as needed. Babcock say they have already had interest from overseas and have potential customers for Arrowhead. Export success for the Type 31e may range from constructing complete ships in the UK, through to just supplying the design and expertise to overseas customers. Almost every nation will have different requirements for warship imports and usually want to involve their own domestic industry as far as possible. The Indonesian Navy is currently in advanced negotiations with OMT to build two frigates based on a variant of the Huitfeldt design in a $730M programme.

Thales has several large manufacturing sites in the UK and has recently decided to move its main development site for the TACTICOS combat management system (CMS) from the Netherlands to the UK.

Thales TACTICOS CMS is a central part of the Arrowhead bid. From an RN perspective, TACTICOS has been seen as something of an outsider with BAES supplying the CMS throughout the fleet. This dominance was recently eroded when Thales won the contract to fit its M-Cube CMS to RN minehunters. TACTICOS is already installed on 180 naval vessels worldwide and is a realistic option for the RN which is trying to be more agile in its acquisition of combat systems. For operators already familiar with the warfare doctrines, the learning curve and training requirement would not be too demanding.

In conclusion

For all the Type 31s competitors the price ceiling remains the challenge. The Danish Navy was able to reduce costs by using cheap Eastern European shipyards for fabricating steelwork, re-using some weapons from decommissioned warships and employing their own navy personnel to do systems integration work. Arrowhead does not have these options but this is offset by a simpler baseline weapons and sensor fit. They will not be specific, but Babcock says some equipment will be furnished by the MoD and are confident they will meet the price target. Arrowhead 140 is undoubtedly a very credible competitor that leverages the many advantages inherent in bigger warships.