Weaponry

Torpedo weapons
The main armament comprises six 53-cm wire-guided torpedoes, each with an effect on target sufficient for sinking a large destroyer. The torpedoes are controlled from the command cen-tre with a central processing unit, TORPE 677B (supplier’s designation is 9 TORCI 104 B).
The target tracker of the system is continually provided with data of the bearing and range to the target. Radar information is obtained from the artillery fire-control unit ARTE m/62 or the navigation radar PN 610.
Target indication is done either from the main indicator or from the target tracker. It is also possible to track the target from command & control indicator, SLI.

Target acquisition can be done manually or automatically. The target tracker evaluates target course and speed. Values for torpedo launching are continually calculated uisng calculated target data from the target tracker, manual inputs of torpedo data, and information of the own ship’s course and speed.
The launching process is controlled and monitored from a control unit, and the desired launching program is set on a program selector. After launching a salvo of torpedoes, they are guided to a parallel course by a program unit in the program selector. When a parallel course has been assumed, the torpedoes of the salvo can be guided manually or automatically to the target.

Artillery weapons
For self-defence and engagements against small vessels, the Spica carries a remote-controlled Bofors 57-mm dual-purpose gun, originally a gun of the model year 1950.
Bofors increased the 40-mm calibre of old guns to 57 mm, which also increased the projectile weight from 1 kg to 2,6 kg, while the muzzle velocity Vo (the projectile velocity out of the barrel) had to be reduced from 1000 m/s to 880 m/s.
Cartridges are fed into the gun from above with a manual feeding device. The barrel has liquid cooing.

In 1975 the 57-mm automatic gun m/50 was replaced by a more modern gun, designated “Bofors 57 mm apjäs 7101”, which is a dual-purpose gun with very good aiming characteristics and capable of high-rate instant firing. Owing to its low overall weight (6500 kg), this gun is especially suited for small vessels.
The excellent multi-target properties are offered through a large elevation range and an unlimited range in traverse. The gun has separate electro-hydraulic laying gears for moving in elevation and traverse, and is normally remote-controlled from a fire-control instrument. Alternatively, the gun can be fine-aimed on the target under gyro stabilization by means of a laying handle, a so-called joystick, on a panel left of the gun.

The elevating system has a 4-compartment magazine for maximum 40 cartridges. Refilling of the magazine and ammunition racks, with a total capacity of 128 cartridges, is done manually. First the gun is slewed to loading position, and then the cartridges are manually moved in a bucket-brigade line from the ammunition supply under the gun to the traverse laying system.
The crew of the gun normally comprises three men on the platform, one gun commander and two loaders, but optionally the gun can be unmanned and be operated under remote control.
Ammunition types used are anti-surface ship shell, high-explosive shell, and pellet-filled explosive shell. Dummy shells for firing exercises are available, with the same ballistic properties as live ammunition.

Fire-control system
The gun is controlled from the first digital fire-control system ever used by the Swedish Navy. That equipment, in the Navy known as ARTE 62, was made by the Dutch company HOSA (Hollandse Signaalapparaten; supplier’s designation M 22/3-52Z) and is a combined system for target indication and fire control.

The radar unit is used for fire control of both artillery and torpedo engagements. The reconnaissance radar of the system is also usable as navigation radar.
Firing data is computed by digital data processing, which gives great accuracy and fast computation, plus options of automatic functions to replace manual operations. Antennas for reconnaissance and fire-control functions are built into a common stabilised unit housed in a radar-transparent plastic bulb (radome) that protects the antennas and enables a controlled environment since the radome can be dehumidified, heated, and de-iced.

The indicator unit, with PPI-screen, radar indicators, and control panel is divided into sections: one sea-target section receiving values from the reconnaissance antenna; one target-indication section with PPI-screen; and one anti-aircraft section getting values from the fire-control antenna.
Firing data for aerial targets and surface targets is computed in parallel by the built-in computer in the indicator. Consequently, firing at one of the targets is possible while making preparations to fire at the other target.
Aerial targets are presented on an A-indicator and naval targets on a B-indicator. “Roller balls” are used for target indication of naval and aerial targets, and for fine adjustments during tracking of naval targets. The roller balls enable fast adjustments of range and bearing values.

Because of her modern radar and fire-control systems, the Spica can use all her weapons in-dependent of daylight and visibility conditions.

Mines, depth charges
Owing to her stable hull, the Spica is an excellent platform when to carry and lay mines. The ship can be configured for a large or a small mine version if taking ashore the four aft torpedo tubes (small mine version) or all torpedo tubes (large mine version).
The mine rails extend on the main deck from the forecastle deck to the stern, on starboard as well as port. Exit rails on the mine tracks are located at the stern.
It is also possible to use the mine rails for carrying and throwing depth charges, but it should be noted that the Spica has no built-in devices for sub-marine chase.

Rocket launchers and rocket beddings
Despite the installed modern radar equipment, the rocket-flare weaponry on board the Spica was saved for use as battlefield illumination.
The Spica has two double launching rails for 103 mm rockets and one gun for 16 rockets of calibre 57 mm. The 103 mm rails were dis-mounted during the 1980’s, but the 57 mm rocket-launching gun was preserved, though now intended for chaff rockets that can be launched to mislead any enemy radar reconnaissance.