The rank of sub-inspector was introduced into the Metropolitan Police in the late 19th century. It did not last long, being effectively replaced by station sergeant in 1890. Officers who already held the rank retained it, and were promoted to inspector as soon as a vacancy arose.
Canada
The Royal Canadian Mounted Police rank of sub-inspector was introduced in 1942 with the insignia of one star, similar to an Army second lieutenant. This was changed in 1960 to three stars, similar to an Army captain. It was disestablished in the reorganization of 1990, which eliminated the RCMP's subaltern ranks.
The rank of sub inspector was replaced after the Rhodesian Unilateral Declaration of Independence with three grades of Patrol Officer, Senior Patrol Officer and Section Officer with one, two, and three gold coloured bars respectively.
India
A sub-inspector is generally in command of few police personnel. He is the lowest ranked officer who under Indian Police rules and regulations can file a charge sheet in court, and is usually the first investigating officer. Officers subordinate to him cannot file charge sheets, but can only investigate cases on his behalf. He can be the station officer in some of the states like Kerala. A sub-inspector ranks above an assistant sub-inspector of police and below an inspector. Most sub-inspectors are directly recruited into the police and have better educational qualifications than lower-ranking police officers. Specialised units such as the Central Armed Reserve Police Force, State Armed Reserve Police and Armed Battalions use the same rank, but generally these officers do not have any investigative powers. There are also specialist non-investigative officers in other Indian law enforcement agencies, such as sub-inspector and sub-inspector. The rank insignia for a sub-inspector is two stars, and a red and blue striped ribbon at the outer end of the shoulder straps. This is similar to the insignia of a subedar in the Indian Army. The assistant sub-inspector will have one star, and a red and blue striped ribbon at the outer end of the shoulder straps. This is similar to the insignia of a naib subedar in the Indian Army. The rank insignia for principal sub-inspector and additional sub-inspector are one and the same. For the post of Sub Inspector and Assistant Sub Inspector, Staff Selection Commission recruits eligible candidates on national level in various Central Armed Police Forces like CRPF, ITBP, CBI, SSB CISF, BSF and SI. In 2017 total number of vacancies announced by SSC in CPO SI was 2221. Apart from SSC, all states government police departments conduct examinations to recruit Sub Inspectors.
Malaysia
In the Royal Malaysia Police, the rank of sub-inspector is the senior-most of non-commissioned officers. They are also the lowest ranking police officers to wear their rank insignia on epaulettes on both shoulders. A sub-inspector of the PDRM ranks immediately above a Sergeant Major and below a Probationary Inspector.
Nepal
In Nepal Police, the rank of Sub Inspector is generally the next senior rank from Assistant Sub Inspector and is less senior than an Inspector. Members holding the rank usually wear an epaulette featuring two silver stars, the same rank badge as a Sub Inspector in the Armed Police Force.
Sri Lanka
In the Sri Lanka Police Service, sub-inspector of police ranks above that of police sergeant major and below an inspector. Generally an SI would be the officer in charge of a small police station, a detachment of police personal or deputy OIC of a larger police station in a metropolitan area. Most sub-inspectors are directly recruited into the police service as probationary sub-inspectors for one year's training. The basic educational entry requirement is that an applicant has passed the G.C.E Advance Level Examination. Annually certain number Other Officers who have come up through the ranks are promoted to rank of SI. The rank insignia for a sub-inspector is one star.
Romania
In the Romanian Police, subinspector is the lowest commissioned rank, below inspector, and corresponds to the former rank of police second lieutenant.
