The Oksoy and Alta class mine warfare vessels were built by Kvaerner Mandal (now Umoe Mandal). The first four ships, Oksoy, Karmoy, Maloy and Hinnoy, which were commissioned into the Royal Norwegian Navy in 1994 and 1995, are minehunters. Five Alta class minesweepers ships, the Alta, Otra, Rauma, Orkla and Glomma, were commissioned in 1996 and 1997.
Only the Alta and Otra remain in service. In November 2002, KNM Orkla (M353) was destroyed in a fire off the Norwegian coast. Rauma and Glomma were decommissioned in 2004.
Kongsberg Defence & Aerospace was awarded a contract in June 2008 to supply a new command and control system for the Oksoy and Alta vessels, for delivery by 2012.
Catamaran hull design
The vessels are of catamaran design, the hull is constructed from a fibre-reinforced plastic sandwich. An air cushion between the two hulls is created as the catamaran moves through the water.
The catamaran structure gives a high transit speed to the area of operations, low magnetic and acoustic signatures and low susceptibility to the shock of exploding mines.
The ship’s surface-to-air missile system is the Sadral twin launcher supplied by MBDA (formerly Matra Bae Dynamics) and armed with the Mistral missile. The Mistral missile is fitted with a 3 to 5 micron infrared and ultraviolet seeker head, a 3kg warhead with impact and laser proximity fuses and SNPE rocket motors. The missile has a range of 4km and approaches the target at a speed of Mach 2.6.
The ships are also armed with one or two 20mm Rheinmetall guns and two 12.7mm machine guns.
The minesweepers are equipped with traditional Oropesa mechanic sweep, a Kongsberg Defence & Aerospace (KDA) Agate (Air Gun and Transducer Equipment) acoustic minesweeping system, and Elma magnetic sweepers.
AGATE generates the acoustic signature of any ship in order to trigger acoustic mines. It uses airguns to generate low frequency sound and transducers to generate the medium and high frequency sections of the noise signature. Minesweeper mini torpedoes can be carried.
The minehunters are equipped with two Pluto remotely operated mine disposal vehicles supplied by Gaymarine in Turate, Italy and by Gayrobot in Balerna, Switzerland. The vehicles are stored in the hangar at the aft deck and are launched by two hydraulically operated cranes. A data link between the host ship and the submersible vehicle is via an umbilical cable.
The vehicle carries sensor equipment selected for the operation, for example a colour camera with black and white low light-level modes, search sonar, scanning sonar and measuring systems for minehunting and mine identification. The electronic package can provide automatic depth, course and speed control and the vehicle’s maximum speed is up to 4kt.
The control console on the ship is equipped with a monitor that displays the camera and sonar image and data from the submersible, including the depth and compass bearing. The displayed data can be recorded for mission analysis.
HUGIN mine reconnaissance system
The Royal Norwegian Navy is undertaking a programme to develop the HUGIN mine reconnaissance system (MRS), to be deployed on Oksoy minehunters.
The system includes the HUGIN 1000 autonomous underwater vehicle (AUV), developed by the Norwegian Defence Research Establishment (FFI) and Kongsberg Maritime. The first HUGIN 1000 was delivered to the RNoN in February 2004. It is based on HUGIN AUVs in commercial use for offshore oil and gas surveying, one of which was deployed aboard KNM Karmoy in 2002/03. A second HUGIN 1000 was ordered in June 2005 and was delivered in January 2007.
HUGIN 1000 has an operating depth down to 1,000m and has an advanced Kalman filter-based aided inertial navigation system (AINS). The AUV can carry payload sensors including synthetic aperture sonar (SAS) or side-scan sonar, multibeam echo sounder, sub-bottom profiler, conductivity, temperature and depth (CTD) sensor and volume search sonar.
A full-capability production model of the HUGIN 1000 will include a high-resolution interferometer SAS sonar system.
Alongside the HUGIN programme, Kongsberg and the Norwegian Defence Research Establishment are developing the Minesniper low-cost mine disposal system for Oksoy / Alta vessels.
Minesniper is a remotely controlled submersible vehicle which is 2m long and weighs about 30kg. It is controlled via a fibre-optic tether and can be fitted with either shaped charge or semi-armour-piercing warheads. Minesniper has a maximum range of 4,000m and a maximum speed of 6kt.
Minehunting and sonar systems
The minehunters are equipped with the hull-mounted TSM 2023 minehunting sonar supplied by SATSA (consortium between Simrad Albatross and Thales Underwater Systems (formerly Thomson Marconi Sonar). The sonar is used for mine detection and classification.
In detection mode the sonar is electronically steerable through 360° and covers a bearing of 90°. In classification mode the sonar uses three different frequencies for shadow analysis. The sonar operator uses two TSM 2023 consoles, one for detection and one for classification.
The minesweepers are fitted with SA 950 hull-mounted sonar supplied by Simrad Subsea AS based at Horten.
The SA950 is an active sector scanning sonar operating at high frequency (95kHz), with high-resolution multi-beam mode for detection of moored and bottom mines. The echoes from the 32 beams are displayed on a high-resolution colour monitor.
In March 2007, Thales Underwater Systems was awarded a contract for the replacement hull-mounted sonar, the TSM2022 mk3 N, for all six Oksoy / Alta vessels. TSM2022 mk3 N is a modular system which can perform mine avoidance functions while minesweeping as well as minehunting and route survey. The real-time synthetic aperture sonar has a route survey mode with high track resolution. Thales was contracted to supply the TSM2061 mkIII command and control MCM software package.
The ship is equipped with two Thales (formerly Racal) navigation radars operating at I-band and a Trimble positioning system with an integrated satellite global positioning system.
The ships are equipped with two MTU 12V 396 TE84 diesel engines each providing 2.7MW sustained power. Fine manoeuvring and stationkeeping is achieved with two Kvaerner water jets. The ship also has two lift diesel engines, type MTU 8V 396 TE54. The propulsion system enables a maximum speed of 23kt and range of 1,500 miles.
The Oksoy and Alta class ships are fitted with a Simrad Albatros Dynamic positioning and tactical system.