Primary responsibility for the maintenance of public order through enforcement of the kingdom's laws was exercised by the Thailand National Police Department (TNPD), a subdivision of the Ministry of Interior. Charged with performing police functions throughout the entire country, the TNPD was a unitary agency whose power and influence in Thai national life had at times rivaled that of the army.

The formal functions of the TNPD included more than the enforcement of laws and apprehension of offenders. The department also played an important role in the government's efforts to suppress the remnants of the insurgency. In the event of an invasion by external forces, much of the police force would come under the control of the Ministry of Defense to serve with, but not be incorporated into, the military forces.

Originally modeled on the pre-World War II national police force of Japan, the TNPD was reorganized several times to meet changing public order and internal security needs. American advice, training, and equipment, which were provided from 1951 through the early 1970s, did much to introduce new law enforcement concepts and practices and to aid in the modernization of the TNPD. During this era the strength and effectiveness of the police grew steadily.

All components of the police system were administered by the TNPD headquarters in Bangkok, which also provided technical support for law enforcement activities throughout the kingdom (see fig. 20). The major operational units of the force were the Provincial Police, the Border Patrol Police (BPP), the Metropolitan Police, and smaller specialized units supervised by the Central Investigation Bureau.

In mid-1987 the total strength of the TNPD, including administrative and support personnel, was estimated at roughly 110,000. Of this number, over one-half were assigned to the Provincial Police and some 40,000 to the BPP. More than 10,000 served in the Metropolitan Police. Quasi-military in character, the TNPD was headed by a director general, who held the rank of police general. He was assisted by three deputy directors general and five assistant directors general, all of whom held the rank of police lieutenant general. Throughout the TNPD system, all ranks except the lowest (constable) corresponded to those of the army. The proliferation of high ranks in the TNPD organizational structure, as in the military, indicated the political impact of the police on national life.

Data as of September 1987