Special Investigation Branch (SIB) was the name given to the detective branches of all three British military police arms: the Royal Navy Police, Royal Military Police and Royal Air Force Police. It was most closely associated with the Royal Military Police, which had the largest SIB. SIB investigators usually operated in plain clothes, although they did wear uniforms when serving overseas. Members were usually senior non-commissioned officers (sergeants or petty officers or above) or commissioned officers, although the Royal Air Force SIB was open to corporals — the most junior NCO rank — and above. In December 2022, the Defence Serious Crime Unit was enacted which replaced all three service SIBs. Royal Navy Police SIB The Royal Navy SIB is the smallest of the three SIBs, with the SIO holding the rank of Lieutenant Commander. They investigate: all incidents falling within Schedule 2 of the Armed Forces Act 2006; Level 3/4 investigations; circumstances prescribed in accordance with the Armed Forces Act 2006; complicated cases involving multiple units (for instance, assaults involving a large number of personnel from different ships). Royal Military Police SIB Although an SIB appears to have existed in the British Army of the Rhine in Germany between 1919 and 1926, the origins of the army's SIB are in 1940, when twenty Scotland Yard detectives were enlisted in the Corps of Military Police to deal with the pilfering of military stores within the British Expeditionary Force (BEF) in France. The unit was formed on the recommendations of Detective Chief Inspector George Hatherill (who later went on to investigate the serial killers John Reginald Christie and John George Haigh, and the Great Train Robbery) and command was given to Detective Superintendent Clarence Campion, head of Scotland Yard's Criminal Record Office, who was commissioned as a Major. Campion was hit in the head by shrapnel during the Dunkirk evacuation and died on 20 May 1940, the only SIB casualty of the BEF. After this beginning, the SIB was established on a full-time basis. One of the first group of detectives, Frank Elliott, was sent out to Cairo, Egypt. Under the supervision of Colonel Claude Harper, Elliott managed a 500-man force which investigated crime in Egypt, Palestine and later Libya. The SIB (RMP) now consists of about three hundred personnel, including Scenes of Crime Officers and forensic technicians. It is divided into numbered units called Investigation Platoons (for instance, 33 Inv