Corvettes date as far back as the "Age of Sail" where their speed, agility and modest firepower were put to excellent use. During the period, the type was constructed larger than a "Sloop-of-War" yet smaller than existing frigate models. The corvette has been carried over into the modern age of steel warships and now exhibits a size larger than coastal patrol craft and may or may not be dimensionally smaller than frigates - the lines between these two ship types becoming more blurred with each passing decade.
The Swedish Navy adopted a corvette vessel through the five-strong Visby-class led by the HSwMS Visby (K31). The class was originally intended to support six such vessels though the final form - the HSwMS Uddevalla - was cancelled. This has left the class with the HSwMS Visby (K31), the HSwMS Helsingborg (K32), the HSwMS Hamosand (K33), the HSwMS Nykoping (K34) and the HSwMS Karlstad (K35). The HSwMS Visby saw her keel laid down on February 17th, 1995 and she was then launched on June 8th, 2000. The vessel remains in active service with the 4th Naval Warfare Flotilla (2013). She was built at the Kockums AB shipyard at Malmo, Sweden - a German-owned firm under the ThyssenKrupp Marine Systems product banner.
The Visby-class of ships share many common traits including weaponry, propulsion and stealth characteristics. Armament is centered around 1 x 57mm Bofors Mk 3 deck gun and 8 x RBS15 Mk 2 series anti-ship missiles (AShM). The Bofors Mk 3 was introduced in 1995 and holds origins in the excellent Mk 1 series debuting in 1964. The RBS15 missile is produced by Saab Bofors Dynamics and is a "fire-and-forget" anti-ship (AS) missile with land-attack capabilities as well - giving the missile a "dual-role" battlefield existence. The weapons are governed by the Ceros 200 Fire Control Radar System (FCRS), the Condor CS-3701 Tactical Radar Surveillance System (TRSS) and an Ericsson Sea Giraffe ABM 3D processing suite. The Combat Information Center (CIC) is set at amidships under the bridge superstructure. Additional sensors are provided through a hull-mounted sonar array, a towed sonar array (at stern) and a variable depth sonar (VDS) system (at stern) to counter the threat posed by enemy submarines. The crew can also call upon an integrated countermeasures suite that includes the Rheinmetall Waffe Munition MASS (Multi-Ammunition Softkill System) decoy system. ECM (Electronic CounterMeasures) chaff launcher is set aft of the deck gun and a radar warning system is fitted to the mast via a radome assembly. The Visby-class can also dispense naval mines and depth charges if need be and is outfitted with torpedoes (4 x 40mm launchers, Type 45 torpedoes) at the stern sides making her a truly multi-role performer. The Visby can also launch and retrieve Remotely-Operated Vehicles (ROVs) for minehunting and mine neutralization actions.
The Visby-class, at one point, was to support 8 x Umkhonto Surface-to-Air-Missile (SAM) launchers and 2 x 6 127mm ALECTO anti-submarine rocket launchers though these have since been cancelled.
Propulsion for the class is governed by a CODAG (COmbined Diesel And Gas) arrangement in which the diesel and gas systems are integrated in such a way so as to provide a maximum power drive through integral management of a diesel and gas turbine arrangement. CODAG allows a surface warship to achieve a maximum straight line speed well above that of their listed cruise speeds through the combined engine configuration governed through a multi-speed gearbox (or several). Diesel engines typically feed into the gearbox, which are also fed by a gas turbine, and it is this gearbox that then drives the propellers directly. This arrangement produces an increase in speed by as much as 10 knots depending on the vessel and operating conditions. The Visby is completed with 2 x low-speed MTU Friedrichschafen 16V 2000 N90 diesel engines rated at 1,300kW each and built into noise-absorbing housings. These are coupled to the required reduction gears which also connect to 4 x Honeywell TF50A gas turbines of 4,000kW each. Three generators provide an additional 270kW of power each. Maximum speed in this configuration is approximately 40 knots. Exhaust outlets are heavily concealed at the stern. 2 x KaMeWa 125 waterjet propulsion "buckets" are provided at the stern for precise handling. Range is roughly 2,500 nautical miles when cruising at 15 knots providing the Visby-class a solid reach and operational radius. The onboard navigation radar is retractable.
Like many other modern warships, the Visby makes extensive use of angled, covered services about her hull design. This approach to "stealth" on the high seas eliminates the use of crevices and vertical faces so common to shipbuilding in decades past. The end result is a clean and well-contoured design intended to reduce radar signatures from prying enemy systems. While not truly making the ship invisible, the vessel nonetheless maintains a harder-to-detect presence. Additionally, the deck gun can be stowed within a forward housing to further reduce the side profile signature. The bridge is set high atop a pyramidal-type superstructure with a commanding view of the action all-around the vessel. Any smoke funnels are purposely left short and enclosed within the superstructure. A radar array (director) is set ahead of the bridge and aft of the deck gun. The mast is also completely enclosed and sections of rail are only present about the aft portions of the ship, both at the superstructure and at the stern deck. The stern deck is home to a helicopter landing deck which can support up to a medium-lift helicopter type airframe. All helicopter-related equipment can be taken down for preserve stealth. A helicopter "bunker station" is fitted to the aft section of the superstructure. RHIBs (Rigid-Hull Inflatable Boats) are carried as well and can be launched and retrieved as needed.
The HSwMS Visby is typically crewed by 43 personnel made up of 27 officers as well as 16 conscripted service members. She displaces at 650 tons and showcases a running length of 72.6 meters, a beam (width) of 10.4 meters and a draught of 2.5 meters - the latter quality allowing the ship to operate off-shore. The vessel is purposefully designed for both close-to-shore (littoral) and deep sea operations allowing her to partake in international efforts as they arise. While her armament is limited when compared to modern missile-minded frigates, it is nonetheless practical and ensures the vessel retain her agility and speed in open water. Additionally, the type's enhanced endurance allows for the ship to stay on station longer than other smaller classes (as well as conduct a quick exit if need be). In this way, the Visby can be used across all manner of missions including at-sea rescue (downed airmen, humanitarian, etc...), anti-piracy service, customs regulation, maritime law enforcement, interception of both large and small craft and as a fast assault platform. The Visby-class can also operate independently or as part of the main Swedish / United Nations-sponsored naval force.