Number 120 Squadron or No. CXX Squadron is a squadron of the Royal Air Force which was established as a Royal Flying Corps unit late in World War I, disbanded a year after the end of the war, then re-established as a RAF Coastal Command squadron during World War II. Although disbanded again a month after Victory in Europe Day, during and after World War II it operated almost continuously, with maritime patrol aircraft; most recently with the Hawker Siddeley Nimrod, based at RAF Kinloss in Scotland until the type's withdrawal in March 2010. The squadron was disbanded again the following year. No. 120 Squadron stood up again in April 2018 at RAF Lossiemouth and became the first squadron to be equipped with the Boeing Poseidon MRA1 anti-submarine warfare (ASW) aircraft on 31 October 2019.

The Boeing P-8 Poseidon is an American maritime patrol and reconnaissance aircraft developed and produced by Boeing Defense, Space & Security, and derived from the civilian Boeing 737-800. It was developed for the United States Navy (USN).