The Transjordan Frontier Force was formed on 1 April 1926 as a para-military border guard to defend Trans-Jordan's northern and southern borders. The TJFF was also an Imperial Service regiment whose Imperial Service soldiers agreed to serve wherever required and not just within the borders of their own colony, protectorate or, in the case of the Transjordan, mandate. This was in contrast to the Arab Legion, which was seen more as an internal security militia, deriving from the troops of the Arab Revolt and closely associated with the Hashemite cause. The Amir Abdullah was an Honorary Colonel of the Trans-Jordan Frontier Force from its inception.
The Transjordan Frontier Force (TJFF) was established at Sarafand on 1 April 1926 with a cadre drawn from the Arab Legion and quickly grew to three cavalry squadrons, each of 120 men each, and an infantry unit. Its first commander was Lieutenant-Colonel Frederick William Bewsher. Other units, such as a camel squadron and mechanised units, were subsequently added.
The TJFF would be equipped in a conventional manner, with modern weapons, whilst the Arab Legion would, initially, remain a traditional force, looser in structure and without training in alien technology. Accordingly, the Arab Legion transferred its inventory of machine guns, artillery, and radios.
The TJFF replaced the disbanded British Gendarmerie which previously had the task of protecting Transjordan's borders.
In the post-World War II era, with the independence of the Transjordan and of Palestine looming, there was no longer a requirement for an Imperial Service unit in the region. On 9 February 1948 the 3,000 man Trans-Jordan Frontier Force was disbanded and most of its members transferred to the Arab Legion.
The TJFF served under Headquarters, British Forces, in Palestine and Trans-Jordan, from 3 September 1939 until 9 February 1948. The O.C. TJFF was a British lieutenant colonel, with headquarters at Zerqa. Second-in-command was a British major, responsible for administration, workshops, quartermaster's stores and pay. The adjutant, another British major, was responsible for training and personnel and was aided by an assistant adjutant who was an Arab officer.