İstif-class (I-class)

The İstif class (also designated the Istanbul class, MILGEM II, or TF-100 class) is a series of multirole frigates developed under the MILGEM national warship program for the Turkish Naval Forces of Turkey and the Indonesian Navy of Indonesia. The program represents the second development phase of the MILGEM project, extending the structure of the preceding Ada-class corvette to incorporate multi-role capabilities. STM serves as the designer and prime contractor, with construction distributed across four Turkish shipyards: Istanbul Naval Shipyard, Anadolu Shipyard, Sedef Shipyard, and Sefine Shipyard.

The İstif class is propelled by a combined diesel and gas (CODAG) propulsion system comprising one General Electric LM2500 gas turbine and two MTU diesel engines driving two controllable pitch propellers. For aviation support, the frigates feature an aft flight deck and a hangar capable of accommodating S-70B Seahawk helicopters and unmanned aerial vehicles such as the KALKAN VTOL or Alpin 2. Combat operations are coordinated by the network-centric ADVENT Combat Management System. Sensor systems include the Aselsan Cenk-400N search radar, ALPER-200N surface radar, AKREP-300N fire control radar, PIRI-100 infrared search and track system, and FERSAH 100N/MF hull-mounted sonar. Electronic warfare is managed by the Aselsan ARES 2N/NGE electronic support measures and AREAS 2NC/E electronic countermeasure systems.

The armament of the İstif-class frigates includes 16 canister-launched Atmaca anti-ship missiles. Air defense is provided by a 16-cell MiDLAS vertical launching system capable of deploying Siper Block 1 and Hisar-D RF surface-to-air missiles; the latter can be quad-packed with four missiles per cell. The primary gun is a bow-mounted 76 mm weapon; the lead ship carries an Italian OTO Melara 76 mm Super Rapid gun, whereas subsequent hulls are fitted with the Turkish-made MKE 76 mm/62-caliber gun. Close-in defense consists of a 35 mm dual-barreled Aselsan GOKDENIZ close-in weapon system utilizing ATOM airburst ammunition, alongside two Aselsan SMASH 200/25 remote controlled weapon stations. Anti-submarine weapons consist of two twin 324 mm torpedo launchers firing Roketsan Orka or MK-46M5 torpedoes.

Steel cutting for the lead ship of the İstif class, TCG Istanbul (F 515), occurred on 19 January 2017. The frigate was laid down on 3 July 2017, launched on 23 January 2021, and commissioned into service with the Turkish Naval Forces on 19 January 2024. Subsequent ships are in various stages of construction or planning. TCG İzmir (F 516) was launched on 10 January 2025, TCG İzmit (F 517) on 11 January 2025, TCG İçel (F 518) on 1 September 2025, and TCG Akdeniz (F 519) on 2 February 2026. TCG Karadeniz (F 520) is currently under construction, while TCG Ege (F 521) and TCG Marmara (F 522) are planned. Internationally, Aselsan's 2023 annual report noted the export of an İstif-class frigate to an unnamed Middle Eastern country. Indonesia signed a contract for two frigates on 26 July 2025, with an agreement signed in January 2026 for Barzan Holdings of Qatar to provide financing to supply TCG İzmir and TCG İçel to the Indonesian Navy, although negotiations regarding this transfer continue.