and further boats were planned for the Pacific and Baltic Fleets. In June 2022 an unconfirmed report from within Russia's defence industry suggested that a further tranche of six additional Project 636.3 vessels might be ordered to start construction in around 2024. The PPK-class "is slightly longer in length — the sub’s submerged displacement is around 4,000 tons — and feature improved engines, an improved combat system, as well as new noise reduction technology; it can fire both torpedoes and cruise missiles, launched from one of six 533-millimeter torpedo tubes." It was reported in September 2022 that a feature of the Kilo class is that they only can carry four Kalibrs, and can only launch the cruise missiles through two of their six torpedo tubes. The PPK class has a seven-bladed propeller, instead of the six-bladed propeller of the Project 877 class. Variants As early as 2009 one Kilo-class submarine, , was equipped with pump-jet propulsion. Operational history In 2015 five Kilo-class were deployed to the Russian Port of Tartus. At least two of the units reportedly attacked land targets inside Syria with M-54 Kalibr cruise missiles (NATO designation: SS-N-27A “Sizzler”). On 8 December 2015 marked the first time a Kilo Class fired cruise missiles against an enemy. The Rostov-on-Don (B-237) earned the honour. Two targets near the ISIS capital of Raqqa were struck by the missile attack. Several of these craft were involved in the April 2018 skirmish with NATO ships in the eastern Mediterranean. The B-237 transited the Dardanelles on its way back to the Black Sea on 12 February 2022. After the sinking of the Moskva, it was remarked that the Kilo-class subs were the only members of the Black Sea Fleet whose orders seemed not to prohibit venturing into Ukrainian waters near Odessa. The Alrosa pump-jet Kilo-class, which derives from the Project 877 hull, participated in the 2022 Russian invasion of Ukraine. This hull was retro-fitted for the Kalibr missile. In September 2022 after the early 2022 Crimea attacks, the UK MoD said that the Kilo-class submarines were moved from Sevastopol to the Port of Novorossiysk in Krasnodar Krai. Operators The first submarine entered service in the Soviet Navy in 1980, and the class remains in use with the Russian Navy today; 14 original Kilo-class vessels believed to still be in active service with the Russian Navy, while eight Improved Kilo-class subs had been delivered as