Within the scope of the İClass (also known as İSTİF Class) Frigate Project, the second phase of the MİLGEM Project, the contract was signed on April 12, 2019 (more than 2 years after the start of TCG İstanbul (F-515)’s construction on January 19, 2017) with STM selected as the Main Contractor in 2018 by the SSB, entered into force on September 27, 2019. Launched on January 23, 2021 at Istanbul Naval Shipyard the first ship of the class, TCG Istanbul (F-515), the extended and enhanced version of ADA Class Corvettes, is scheduled to start Sea Acceptance Tests in January 2023 and is planned to enter Turkish Naval Forces (TNF) service on September 6, 2023. According to original plan the TCG Istanbul Frigate was to be inducted into the TNF service in 2021, but this deadline was later extended to September 2023.

The İ Class Frigate Program was launched to construct four frigates to replace aging YAVUZ Class Frigates in mid 2020s. The other three sister ships (TCG İzmir, TCG İzmit and TCG İçel) are planned to be constructed in private shipyards and are expected to be delivered by 2027. For the series construction of the sister ships a tender was launched and Dearsan and TAIS were shortlisted in late 2016. But since then either no selection has been made between these two bidders or the result has not been publicized so far. 

In line with the changing and developing operational requirements of the TNFC, the İ Class Frigates were planned to be equipped with a 16-cell Mk-41 VLS (behind the 76mm Super Rapid main gun on the bow) for a total of 64 ESSM Block I and Block II missiles (to increase anti-air-warfare capability), Phalanx Mk-15 Block 1B Baseline 2 CIWS and 16 Harpoon Block II Surface-to-Surface Anti-Ship Missiles with coastal targets engagement capability. However, due to the CAATSA sanctions that were officially announced on December 14, 2020 by the US Government, the I Class Frigates will feature different weapons and sensor configuration than originally envisaged in the project. The Presidency of Defense Industries (SSB) had assigned Roketsan for the procurement of Mk-41 VLSs from the US and awarded a contract on February 14, 2018 for the procurement of 4 Vertical Launch Systems (VLS) for the İ Class Frigates. The contract became effective on March 15, 2018 and Interface Working Group Meetings were held in June 2018 and January 2019. However, problems were experienced in procurement of both Mk-41 VLS and Mk-15 Block 1B Baseline 2 CIWS systems due to the embargo imposed by the US Congress. The last blow to the supply of these critical defense systems from the US was the CAATSA sanctions. Since the SSB has the status of end-user in these contracts the deliveries were covered by CAATSA sanctions, a decision was made to use the domestic National Vertical Launching System (MDAS, to be integrated with locally developed SAMs), 35mm GÖKDENİZ Close in Weapon System (CIWS) and ATMACA Block I Anti-Ship Missiles (with coastal targets engagement capability) on the İ Class Frigates. The armament will also include the Leonardo 76/62mm Super Rapid (or MKEK’s 76mm naval gun) main gun to be fitted on the bow section and to provide a high rate of fire against air and surface targets, a pair of Aselsan’s 25mm STOP Remote Controlled Stabilized Naval Gun Systems to be deployed at both port and starboard of the ship and a pair of 324mm twin Light Weight Torpedo Tubes (to replace made-in USA Mk32 Mod 9 Surface Vessel Torpedo Tubes) for Mk46 Mod 5, Mk54 and ORKA LWTs.

The I Class Frigates will feature new generation (Networked Capability, higher performance and a shortened reaction time) the GENESIS ADVENT (Network Enabled Data Integrated Combat Management System) Combat Management System (CMS). As a platform-independent CMS “Developed with the Naval Forces for the Naval Forces” and which can be integrated with a wide variety of sensors and weapons, the GENESIS ADVENT is a powerful and scalable C4I System that provides planning, tactical picture compilation, decision-making and weapon control to meet current and emergent threats. The ADVENT CMS, which has been developed in 3 different facilities of ARMERKOM and Havelsan, is one of the most comprehensive Combat Management Systems both in Turkey and the world with approximately 550 applications and 13 million lines of code. The İ Class will also feature the ADVENT LINK, which works under the ADVENT CMS, allowing different communication protocols to communicate with each other. This system supports Link 11, Link 16, Link 22, VMF, FFI and Web Service protocols, as well as the Multi-Link Process protocol that enables Link 11, Link 16 and Link 22 to communicate with each other.

For Anti-Submarine Warfare (ASW/ missions the İ Class Frigates will have the SH-70 ASW/ASUW Helicopter, Aselsan’s FERSAH hull mounted medium frequency active/passive sonar system and new version of HIZIR Torpedo Defense System with a Towed Array containing both low frequency active (DÜFAS, Low Frequency Active Sonar to replace Towed Decoy) and passive sonar arrays/transducers as well as a winch positioned at the stern of the vessel and a pair of expendable acoustic decoy launchers deployed at port and starboard.

The navigation, communication and sensor systems to be installed in the İ Class vessels will include AKREP (AKR-D Block B-1/2) Fire Control Radar, X-Bant SatCom System, LN270 Fiber-Optic Gyros (FOGs), Laser Warning System, IFF System, SeaEye-AHTAPOT EO Reconnaissance and Surveillance System, PIRI-KATS IRST System (dual band [LW & MW] IR Search and Tracking System with 3 antennas each has 120-degree coverage and able to track 150 targets simultaneously), KULAÇ EchoSounder System (depth measurement equipment), MILPARS Electromagnetic Log System, Underwater Telephone and ALPER LPI Navigation Radar. The TCG Istanbul Frigate was planned to be fitted with the SMART-S Mk2 3D Surveillance Radar but as underlined above the ship will be integrated with new indigenous 3D naval surveillance radar. Aselsan previously introduced the HAZAR 3D Naval Radar Family with rotating active phase array antenna for the first time at IDEF ‘13 Fair with a scaled mock-up of the system. It can be produced in different sizes as S-Band and X-Band thanks to its scalable architecture and the HAZAR multi-function rotating/scanning digital AESA radar will feature GaN based solid-state Transmit & Receive (T/R) modules. 

The İ Class Frigates will be fitted with a comprehensive integrated ESM and ECM suite including Aselsan’s ARES-2N Radar ESM (probably the V2 version which features new generation wide-band receivers improving instantaneous band width and receiver parameters) and new generation AREAS-2N Radar EA System. Featuring both wide and narrow band digital receivers, Digital RF Memory (DRFM, for modern coherent threats) and solid-state power amplifiers the AREAS-2N Radar Electronic Attack System will include a total of 4 AESA antennas (each covers 90-degree field of view and incorporates over 1,000 T/R modules) of which two of them will be deployed at port and the remaining two at starboard side of the ship. Thanks to its directional RF radiation capability, which enables deceptive and noise jamming techniques in a dynamic threat environment the AREAS-2N Radar EA System is able to jam/deceive up to 32 threats simultaneously (8 threats per antenna).  At the moment only YAVUZ and BARBAROS Class Frigates of the Turkish Navy have Radar EA capability thanks to their Scorpion 2 Radar EA System. Turkish Navy performed its first ever Radar EA test with Scorpion 2 Radar EA System on board the TCG Turgutreis Frigate against 16 F-16 aircraft of the TurAF in the Mediterranean Sea in 1993 and successfully jammed AN/APG-68 radars of these aircraft (which does not have AN/ALQ-178(V)3 EW Self Protection System at that time). According to a Thales product brochure, performing at 7.5GHz to 18GHz frequency range and providing 360-degree azimuth coverage, the DRFM capable Scorpion 2 is able to generate up to 200kW ERP and able to deal with 6 threats simultaneously.

Modern influence sea mines detect the magnetic disturbance of a vessel in the Earth’s Magnetic Field, this is referred to as the vessels magnetic signature. To minimize this threat naval vessels are fitted with an on-board Degaussing System (DG) that generates reverse magnetic signature. The İ Class Class Frigates will be equipped with a made-in Turkey (TÜBİTAK BİLGEM) Shipboard Automatic Degaussing System. TÜBİTAK BİLGEM’s Shipboard D/G System is already at service on ADA Class Corvettes of Turkish Navy and being integrated also on TCG İstanbul Frigate, first of İSTİF Class Frigates. Armelsan’s ARAS-2023 Diver Detection Sonar is also expected to be installed on TCG Istanbul Frigate. According to Armelsan, ARAS-2023 Diver Detection Sonar (DDS) will be able to detect a diver with closed-circuit breathing system from 450m (900m diameter), a diver with open-circuit breathing system from 800m (1,600m diameter) and Swimmer Delivery Vehicles (SDV) from 1km (2km diameter). The ARAS-2023 DDS’ “wet end” weighs 40kg, has deployment depth of 5-50m and operational frequency of 70kHz with 360-degree acoustic coverage. The ARAS-2023 DDS, which will be integrated to the CMS on board, can be deployed from a crane as well as by hand or it can be secured to the desired location by connecting it to the bottom of the sea with a tripod for port security tasks. The sonar’s communication with the ship (digital data) and energy requirement will be provided via cable.

The İ Class Frigates will have a monohull, displacement-type hull form and. Their overall length is 113.2 metres, waterline length is 105.2 metres, maximum beam is 14.42 metres, draft is 4.05 metres, and displacement is 2.966 tons. The İ Class Frigates will have around 50% increased fuel capacity and cruising range capability compared to ADA Class Corvettes (with 170 tons fuel capacity have a range of 3,500nm with economic speed of 14 knots, but their fuel capacity was later increased to 180 tons). To be powered by two MTU 20V 4000 M93L diesel engines (driving two shafts) and a LM2500 gas turbine (in combined diesel and gas engines [CODAG] configuration) the I Class Frigates will be able to achieve over 29 knots and to have a range of 6,570nm with economic speed (14 knots). The İ Class Frigates will have a large flight deck at the stern to accommodate a 10t-class SH-70 SeaHawk multi-mission naval helicopter. It also will have a large hangar to accommodate the SH-70 helicopter. The ships will have a capacity to carry 2 SH-70s, one in the hangar and one on the deck. The İ Class Frigates have a accommodations designed for 123 personnel