Van Speijk-class

The Van Speijk class consisted of six frigates built for the Royal Netherlands Navy between 1963 and 1968. The design was based on the British Leander-class frigate, selected to expedite construction for the replacement of aging destroyer escorts. These vessels were also intended to assume NATO patrol duties following the decommissioning of the anti-submarine warfare carrier Karel Doorman.

The Dutch configuration utilized the Leander hull and machinery but substituted British electronics and electrical equipment with systems from Dutch manufacturers. The original electronics suite, supplied by Hollandse Signaalapparaten, featured the LW-02 long-range air-surveillance radar, DA-02 medium-range air/surface search radar, and M45 fire control systems. The installation of the M44 radar/visual director allowed for the inclusion of two Seacat missile launchers, an increase over the single launcher found on the original British design.

Beginning in December 1976, the class underwent a mid-life modernization. This process involved replacing the twin 4.5-inch gun turret with a single OTO Melara 76 mm gun and installing quadruple Harpoon anti-ship missile launchers. Anti-submarine capabilities were updated by replacing the Mk 10 Limbo mortar with Mk 32 torpedo launchers. These modifications, along with the relocation of the variable-depth sonar, allowed for an enlarged flight deck capable of operating the Westland Lynx helicopter in place of the Westland Wasp. Sensors were upgraded to LW-03 and DA-05 radars, and the SEWACO V automated combat management system was integrated. Automation of the power plant during this period facilitated a reduction in the total complement.

The Royal Netherlands Navy operated the class from 1967 until 1989. Between 1986 and 1989, all six vessels were sold to the Indonesian Navy, where they were renamed the Ahmad Yani class. Under Indonesian operation, the vessels have undergone further modifications. The Seacat launchers were replaced with Simbad launchers, and the Harpoon missiles were replaced by either Yakhont or C-802 missile systems. In the case of the Oswald Siahaan, vertical launch system cells for Yakhont missiles were installed on the quarterdeck. Between 2003 and 2008, the Indonesian Navy replaced the original steam turbine propulsion with diesel engines. Five units remained in Indonesian service following these refits.