Options abound for RPB armament

The RAN wants its new patrol boats to be armed - but cannot make up its mind what sort of gun to specify.
One of the most contentious issues surrounding the acquisition of the RAN's planned Replacement Patrol Boats (RPB) is the selection of a light naval gun system. Navy is adamant that a minor calibre gun on the RPB is essential. Others, mostly outside the RAN, are not so sure. Opponents to a light naval gun system for the RPBs include, industry sources say, Under Secretary for Defence Mick Roche.

There is an innate recognition of the necessity of a light naval gun system for the RPBs at many levels within the RAN, including the very top. It is acknowledged that without a dedicated, precision direct fire capability the RPBs will be hamstrung in their ability to successfully prosecute some missions.

But according to RPB operational requirements manager Commander Chris White, the RAN is unlikely to specify which particular light naval gun system it wants on the boats. Instead, it will probably specify in the Request for Tender (due for release in July at time of writing) the functionality requirements, leaving it up to individual bidders to respond with what they consider to be the most appropriate light naval gun system solution to meet those requirements.

Even at this late stage, navy is still not clear on which calibre gun it will call for. Informed sources suggest that navy has a clear preference for a 30mm system. The only 30mm guns currently in ADF service are those arming the six Huon-class coastal minehunters. These are Oerlikon 30mm cannons integrated with the MSI-Defence Systems DS30B mount. The RAN is reportedly satisfied with the performance of its DS30B systems thus far. The DS30B, close to 100 examples of which have been sold to seven navies worldwide, is recognised as one of the leading light naval gun systems on the market.

The DS30B mount itself is fully marinised, stabilised and well proven. The DS30B mounts on the Huons are of the LOCSIG type (locally controlled by a single operator). However, as one well-placed industry source told ADM, the problem with the DS30B is not its performance, but its cost. "The mount is costly, the gun is costly and the 30mm ammunition is costly," he said.

While the RAN is known not to be keen on introducing another nature of gun into service, cost is far and away the principal driver behind Sea 1444 and the selection of a light naval gun system, like other areas of the vessel design, is under pressure to produce savings wherever practicable. Studies are currently underway to determine the cost of manufacturing 30mm ammunition in Australia. The study is expected to take into account the feasibility of standardising the RAN's light naval gun system inventory on the DS30B system, thereby increasing the number of weapons acquired and improving the financial case for local manufacture of 30mm ammunition.

Assuming that the RAN acquires 15 RPBs (one DS30B each), two new underway replenishment/oiler ships to replace HMAS Success and Westralia (one each), Tobruk replacement (one), HMAS Manoora and Kanimbla (one each) and the six existing systems on the Huons, the total number of DS30B systems to eventually enter service in the long term could be as high as 26, not including a shore-based training capability. However many RPBs are built, the RAN will require a dedicated crew training light naval gun system at HMAS Cerberus in Victoria. Currently, when crew training on the DS30B systems on the Huons is required, a boat must be taken out of operation as a training gun system was not included as part of the original MHC contract.

To what extent the DS30B's high acquisition cost will be offset by commonality with the Huons and having an established local support facility - ADI Limited - with responsibility for assembly, training packages, documentation, testing, set to work and logistics support is unclear. ADI assembles and manufactures various components of the DS30B mount under licence from MSI and contracts out some work to local sub-contractors.

As for 25mm ammunition, it is significantly cheaper and currently being manufactured by ADI at Benalla. The army will soon have 130 Boeing M242 Bushmaster I 25mm chain guns in service once the full complement of Phase 3 ASLAV-25 wheeled armoured reconnaissance vehicles are delivered.

Another MSI mount, the DS25/30M, is fitted with either a 25mm Bushmaster I or the 30mm Bushmaster II chain gun. The commonality advantage of the DS25M and the Bushmaster Is on the ASLAV-25 is significantly greater than that between the DS30B and the six systems fitted to the Huons. Should navy adopt the DS25M system full advantage will no doubt be taken of the much higher 25mm ammunition consumption by army, therefore reducing the cost of procuring ammunition for navy, particularly for training purposes. The DS30B and DS25M mounts share around 70% commonality.

Should navy opt to retain the 30mm calibre but seek greater commonality savings, the DS30M fitted with the Bushmaster II 30mm weapon may be an option. Bushmaster II has around 85% parts interchangeability with the ASLAV-25's 25mm Bushmaster I. The Bushmaster II also arms the Boeing AH-64D Apache, which is one of the contenders for project Air 87.

While the 30mm Bushmaster II can be integrated with the DS30B mount following modifications, ammunition between it and the Oerlikon KCB cannon on the DS30B is not interchangeable, with each gun firing a different size 30mm cartridge.

In terms of acquisition costs, the 25mm Bushmaster I is said to be priced, depending on the quantity ordered, between A$200,000-$230,000 per gun. The 30mm Bushmaster II costs close to A$300,000 per gun, while the Royal Ordnance produced 30mm Oerlikon KCB costs around A$350,000 per gun.

Ballistically, the 30mm round enjoys greater range and terminal effectiveness/lethality in both the anti-surface and anti-air roles than 25mm projectiles. However, 25mm weapons generally carry more ready-use ammunition on the mount than 30mm systems. For example, the DS25M mount carries 270 rounds of 25mm ammunition, while the DS30B/DS30M mounts each carry 160 rounds of 30mm ammunition.

The RAN has shown some interest in a remotely operated system for the RPBs, but cites disadvantages such as higher acquisition costs and the lack of a vessel combat system to "plug into". Candidate remote systems could include the Kollmorgen Electro-Optical/MSG Mk 98 Mod (1) 25/30mm naval gun system. This system uses the Bushmaster I or Bushmaster II chain guns. A crew-served version of the Mk 98 is also available.

Other systems which may come under consideration include the 25mm United Defence LP Mk 96 Mod 0 and the 25/30mm Typhoon G from Rafael. Again, both systems utilise the Bushmaster I and II chain guns.

By Ian Bostock, Sydney