The first known legal office was the Advocate of the Army, who prepared cases for prosecution under military law, arranged the summoning of a court martial and administered the oaths of witnesses. The first Judge Advocate General (JAG) was appointed in 1666, and in 1806 the office became part of the Privy Council and was responsible for answering questions on behalf of the government on questions of military discipline raised in Parliament. Legal advice to senior officers by Judge Advocates was available from the Napoleonic Wars but there was little support for soldiers, especially at courts martial, until after the First World War.

During the First World War, pre-trial advice was provided by staff officers in major unit headquarters, but because of the extra work of courts martial and demobilisation at the end of the war Deputy JAGs were appointed to review procedures and supervising officers dealing with legal matters. Legally qualified officers appointed to courts martial duties advised the court on charges and acted as prosecutors or Judge Advocates.

June 1923 saw the formation of the Military Department of the Office of the Judge Advocate General- the Army’s legal department. Its main duties were to advise and assist convening officers on courts martial procedures, provide a prosecuting officer in difficult cases, to advise General Officers on legal questions, to advise and assist with questions raised at Courts of Enquiry, to advise on claims made by the public against the military, and to conduct courses on military law. Soldiers were usually defended by regimental officers and it was unusual for the accused to receive legal advice.

With the declaration of war in 1939, numbers of Army lawyers increased following mobilisation. New officers received instruction on military procedures using a playlet based on courts martial using actors who had enlisted in the Queen’s Westminster Rifles. A branch of the department (the War Crimes Group) was established by the end of the war to the prosecution of war crimes trials, including the investigation into war crimes, giving advice, and sometimes acting as prosecutors.

In October 1948 the Directorate of Army Legal Services (DALS) was formed. Legal aid for soldiers at public expense was introduced in 1950 and the responsibility of administering the scheme led to the formation of Army Legal Aid (ALA), which became part of DALS in the 1970s. DALS became the Army Legal Corps in November 1978. In the 1984 the Police and Criminal Evidence Act (PACE) and the requirement to provide legal advice meant the expansion of the role of the ALS. On operations officers were stationed in theatres, assisting in legal matters, discipline, legal aid, and criminal injuries compensation. They also assisted in POW processing, the distribution of money, and providing advice and instruction on rules of engagement.

The Army Legal Service was disbanded on formation of the Adjutant General’s Corps in 1992.