Izumo class far from carriers in the fullest sense

by | 27th September 2016 | News

Home News Izumo class far from carriers in the fullest sense

Warship Technology: October 2016

When the Japan Maritime Self Defense Force (JMSDF) launched its largest warship since World War II, the ‘helicopter-carrying destroyer’ Izumo (DDH 183) in August 2013, there was little doubt among observers – certainly among the rather outspoken Chinese – that Japan had unequivocally joined the league of aircraft carrier-operating navies. Despite Japanese insistence that the ship – and a pair of smaller but similar Hyuga-class ships – are not aircraft carriers but helicopter-carrying multirole and multipurpose destroyers; the Economist noted at the time that “if it’s as big as an aircraft-carrier and looks like an aircraft-carrier, chances are that it is an aircraft carrier – or can readily be turned into one.”

However, the fact is that Izumo (and sister ship Kaga, which is due to enter service in 2017), are not yet capable of operating fixed-wing aircraft, such as the Joint Strike Fighter (JSF), the F-35B STOVL aircraft. In any event, the F-35B is also not planned for acquisition by the Japanese military. The ships are not fixed-wing strike aircraft-operating aircraft carriers in the traditional sense. In due course they could conceivably operate unmanned aerial vehicles, and although observers agree that they could be converted into a JSF-operating platform with relatively simple modifications to the flight deck and other spaces, this remains a hypothetical capability until F-35B aircraft begin cross decking on the Izumo class.

The JSMDF’s transition to operating flattops has been gradual. Initially, the service operated two classes of destroyers that were capable of embarking three large anti-submarine warfare (ASW) helicopters and operating two simultaneously, starting with the Haruna-class DDH in 1973 and the follow on Shirane class in 1980. Lessons learnt, particularly operational limitations in handling three helicopters with two sets of helicopter recovery and traversing equipment, led to a decision to operate ‘through deck’ destroyers with a minimum of three helicopter landing spots.

This decision would culminate in the induction of the two-ship Hyuga-class DDH, Hyuga and Ise, followed by another, much larger pair – Izumo, and the currently under construction Kaga. The ships have been described as ‘multirole’ and ‘multipurpose’ – that is to say, they have multiple warfighting roles as a helicopter carrier capable of ASW and airborne mine countermeasure (MCM), as command and control platforms for escort flotillas, along with military operations other than war (MOOTW) such as humanitarian assistance and disaster relief (HADR) – a role in which they have been used extensively.

However, before the Hyuga class entered service, the JMSDF commissioned three 178m, 9,000tonne (14,000tonne fully loaded) Osumi-class ‘flattop’ amphibious warfare dock ships with two landing spots. These vessels entered service between 1998 and 2003. The ships no doubt provided valuable design experience and operational insight that informed the design, construction and operation of large helicopter operating platforms.

Hyuga class
The Hyuga class was sanctioned as 16DDH and 18DDH in 2004 and 2006 respectively, the codenames reflecting the corresponding Japanese calendar year. Both were built at IHI Marine United (now Japan United Marine Corporation) in Yokohama at an estimated cost of US$1.1 billion apiece. Keel laying for Hyuga (DDH 181) took place on 11 May 2006, followed by launching on 23 August 2007 and commissioning on 18 March 2009. Ise (DDH 182) was laid down on 30 May 2008, launched on 21 August 2009 and commissioned on 16 March 2011. Production had commenced considerably earlier than the keel-laying milestone. Their names are taken from Imperial Japanese Navy battleships that saw action in World War II.

With a length of 197m, beam of 33m and maximum beam of around 38m, they have a draught of 7m and displace around 14,000tonnes, increasing to 19,000tonnes in fully loaded state. Their complement is around 380 although accommodation spaces are sufficient for around 480 persons. The approximately 195m-long flight deck has four landing spots and two large, 30tonne elevators – a forward 20m x 10m and an aft 20m x13m for aircraft, along with two smaller elevators for weapons and supplies. The hangar, located between the two aircraft elevators is at least 60m long although another estimate suggests a figure in excess of 106m. There is sufficient hangar space to store 11 helicopters. Its dimensions are adequate for the MV-22 Osprey to be hangared. The island structure, with five levels, is about 70m long while the hull has seven levels. Considerable attention has been paid to signature management.

Heat tolerance
The Japanese claim that the flight deck is not designed to withstand the high temperatures associated with jet exhaust from STOVL aircraft like the F-35B, although Osprey operations from this class since 2013, if not earlier, would suggest the deck is capable of withstanding high temperature jet exhaust to some extent – reportedly in excess of 920°C (over 1,700°F) – for limited periods.

The propulsion system is a COmbined Gas turbine And Gas turbine (COGAG) configuration with two propulsion trains, each consisting of two Ishikawajima Harima-built General Electric LM2500-30 gas turbines driving a five-bladed controllable pitch propeller through a gearbox. Maximum speed is in excess of 30knots while range is thought to be 6,000nm at 20knots. A Prairie Masker system to reduce acoustic signatures is standard.

The heart of the ship’s combat system is the advanced technology combat system (ATECS), which is not dissimilar to the US Navy’s Aegis system. It consists of several linked systems including the OYQ-10 advanced combat direction system, the FCS-3 multifunction radar system with separate C-band and X-band (director) fixed arrays mounted on the superstructure, OQQ-21 ASW system, NOLQ-3C EW system along with various communications systems including several satcom systems such as NORA-1C, NORA-7, NORQ-1, NORC-4B; datalinks like the ORQ-1C helicopter data link and tactical data links like Link 11,16 and the USC-42 for joint operations with the US Navy. Radars include OPS-20C navigation radar.

The weapons suite includes two quadpack Mk 41 vertical launch systems (VLS) for 16 Evolved Seasparrow (ESSM) and 12 RUM-139 anti-submarine rocket (ASROC) missiles fitted aft on the flight deck as well as two 20mm Phalanx CIWS – one mounted near the bow on the main deck and the other aft on the port side below the flight deck – along with two HOS-303 triple 324mm torpedo tubes that are in the hull and fire through doors along with a number of 12.7mm machine guns.

The ships are not only meant for ASW but also as command vessels for escort flotillas, as well as for MOOTW, such as HADR, a role in which they have already been used successfully. As a result, the mix of embarked air groups of SH-60K and MCH-101 or other types of helicopter, such as the Chinook, that are embarked at any time is mission dependent. The maximum number of aircraft that can be stowed in the hangar is 11. Clearly, another eight or so helicopters can be stowed on the deck although this is not standard operating procedure in the Japanese Navy.

Izumo class
With the successful experience of the Hyuga class, the JMSDF moved forward with the design and construction of two larger platforms. The first of these, Izumo (DDH 183), then codenamed 22DDH, was authorised in 2010, followed by the second, Kaga (DDH 184), then codenamed 24DDH, in 2012. Their names are taken from a cruiser and carrier of the Imperial Japanese Navy, respectively.

Construction of Izumo began in 2011 at IHI Marine United Shipyard in Yokohama. Keel-laying took place 27 January 2012, launching on 6 August 2013 and sea trials commenced on 29 September 2014 followed by commissioning on 25 March 2015. Kaga was laid down 7 October 2013, launched on 27 August 2015 and it is due to be commissioned in March 2017. The estimated cost of the vessels is reportedly around US$1.5 billion apiece.

The Izumo class have an overall length of 248m, a maximum beam of almost 50m at the flight deck level (although the hull’s beam is 38m), a depth of 33.5m and a draught of 7.5m. Standard displacement is 19,500tonnes increasing to 27,000tonnes fully loaded. The complement is 520 along with sufficient accommodation for another 400-500 troops and 50 3.5tonne trucks which are loaded and unloaded through a ramp on the starboard side. For HADR missions, there are comprehensive medical facilities including a surgery with 35 beds. 

The island structure, including the platforms, with five levels, is about around 70m long. Like the Hyuga class, considerable attention has been paid to reducing signatures. The 243m flight deck allows for relatively unimpeded aircraft movement and is able to simultaneously operate five helicopters. Weapons, except for the forward CIWS on the starboard side of the flight deck, are mounted on hull sponsons or the island structure. Another notable difference from the Hyuga class is the aft 14m x 15m deck edge elevator on the starboard deck edge behind the island structure. The forward 20m x13m elevator remains on the centreline as on the Hyuga class. There are three small elevators for weapons and supplies, two forward, one aft.

Izumo’s hangar is estimated to have almost twice the area of that of Hyuga and there is sufficient hangar space for 14 helicopters. A typical air group is seven ASW helicopters and two search and rescue helicopters. Notionally, more than 25 helicopters could be embarked if deck parking is used.

The COGAG propulsion system is similar to that of the Hyuga class except the LM 2500 gas turbines with integrated electronic controls (IEC) generate 10% more power for a total output of 110,000 shp. Maximum speed is in excess of 30knots. Range is presumably similar to that of the Hyuga class. Four LM500 turbines supply onboard ship service electrical power.

The Izumo class does away with the Mk 41 VLS and ESSM relying instead on the shorter range SeaRAM missile and Phalanx CIWS for anti-missile defences. The ATECS comprises the OYQ-12 combat direction system, OPS-50 AESA radar, OPS-28 surface-search radar, OPS-20 navigation radar, OQQ-23 bow sonar, NOLQ-3D-1 electronic warfare suite as well as various communications and data-link suites like the Hyuga class. Softkill systems include six Mk 137 twin decoy launchers and the OLQ-1 torpedo defence system with anti-torpedo mobile decoy and the floating acoustic jammer (FAJ) sub-systems.

These four ships serve as very useful and capable platforms for (limited) power projection – if attack helicopters are used for example – and MOOTW roles. Although there has been a long-held reluctance from Japan to be seen to be operating any ‘offensive’ platforms, ongoing and planned amendments to Article 9 of Japan’s pacifist constitution – driven in no small measure by rising tensions in the South China Sea and a more aggressive or ‘dynamic’ defence force posture – will certainly inform future developments.

Inherently defensive role
It is not inconceivable that the Izumo class could yet be converted into ‘proper’ light aircraft carriers at some point, although doing so would take considerable time as carrier aviation skills are lacking in the JMSDF. Even so, the ship will remain inherently defensive in nature as the JMSDF will continue to rely on the offensive capabilities of its close ally, the US Navy for the foreseeable future. For now, there are no immediate plans for any more carrier-like ships. Instead the next major JMSDF programme is for a large surface combatant.

As far as the regional balance of power is concerned, the Chinese – who are vociferous in their criticism of the ships – have large carrier programmes of their own, that completely dwarf anything the Japanese currently possess or plan to possess.

Japan’s relations with South Korea, with whom a lingering dispute over small islands continues, is more complex as there is both disagreement and cooperation at the same time. The South Koreans operate a single 200m, 19,000tonne flattop helicopter dock ship (LPH) Dokdo, and they are building a second, somewhat larger version that is thought to be equipped with a ski jump. Taiwan’s plans for a similar flattop LPH remains a dream for now.

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