Many men who had served in the forces during the Great War decided to re-enlist for a short period of service in the Defence Force, which was established in April 1921.

Background
The Defence Force was created as a means for the British Government to overcome an industrial crisis in the coal mining industry and associated railways. The crisis stemmed from the return after the Great War of control of the mining industry to private coal owners. In an increasingly desperate economic slump through 1920, the owners began to propose and impose cuts to miner’s wages by proportions varying from 10% to as much as 49%. The “Triple Alliance” of coal mining unions called for a strike. The crisis threatened to bring the British economy to a standstill. It should also be recognised that the British Government was most concerned to allay the spread of what it saw as “Bolshevism”. The British Government, led at the time by David Lloyd George, prepared to mobilise armed forces to intervene.
On 4 April 1921 the Speaker of the House of Commons read a Royal Message to the Members present in the House:
The Emergency Powers Act, 1920, having enacted that if it appears to His Majesty that any action has been taken or is immediately threatened by any persons or body of persons of such a nature and on so extensive a scale as to be calculated, by interfering with the supply and distribution of food, water, fuel, light, or with the means of locomotion, to deprive, the community or any substantial portion of the community, of the essentials of life, His Majesty may, by Proclamation, declare that a state of emergency exists; and the immediate threat of cessation of work in coal mines having, in His Majesty’s opinion, constituted a state of emergency within the meaning of the said Act: His Majesty has deemed it proper, by Proclamation made in pursuance of the said Act and dated the 31st day of March, 1921, to declare that a state of emergency exists. (Hansard)
On 8 April 1921 the Prime Minister, David Lloyd George, announced to the House that efforts to reconcile difference between mine owners and miners representatives had broken down; and that the Police force was insufficient in size in view of the number of places that would require protection against potential acts of ‘a concerted plan to suspend the principal services [mines, railways etc] that are essential to the life of the community’. He read a message from the King announcing an National Emergency and the mobilisation of Naval and Military Reserves for active service.
Reserves are mobilised
Those men who had a liability as current members of Sections B and D of the Army Reserve, except those resident in Ireland and those already serving in the police, were ordered to report to their normal place of rejoining which was stated on the Protection Certificates they had been issued when transferring to reserve.
Defence Force formed
The Territorial Force was not to be embodied or asked to serve, but members of the TF and other ex-servicemen generally were invited to enlist into a new Defence Force from 9 April 1921. [The Class Z Army Reserve that had been established towards the end of the Great War had been abolished on 31 March 1920 and all Z Reservists had been formally discharged.]
Those men that enlisted into the Defence Force would be engaged for 90 days and would be paid at normal army rates. The recruits would need to be between 18 and 40 years of age inclusive, and be medically fit to serve. Separation allowances would be paid in the case of married recruits aged 26 and above. No uniform was to be issued: men would wear plain clothes and maintain them at their own expense through their service, for which they would be paid a £5 grant. [Later this was converted into a £5 bounty and uniforms were introduced]. They would go to their nearest Territorial Drill Hall for enlistment. All men would be enlisted as Privates: a press report suggested that even a Brigadier-General had done so.
Newspapers across Britain reported that enlistment was brisk, with right-wing political parties, the “British Legion” and the “Middle Class Union”, all being active in encouraging men to join. As an example, the “Western Daily Press” reported 50 men per hour enlisting at the Bristol drill hall used by the 6th Gloucestershire Regiment.
Part of the attestation form of a young man – a coal miner, highly likely to have been a member of a Trade Union – who had served in the Great War, re-enlisting into the Defence Force. It may be that the lure of army pay and separation allowance outweighed for him the possibility of a period of no pay at all during a strike.
The army formed the newly-engaged men into units known as “Number X Defence Unit”, with the number corresponding to the Territorial Force unit to which the nucleus cadre had first been attached.
The newspapers were quick to print a Government rebuttal of rumours that the Force had in fact been assembled in order to put down a rising in Germany.
Meetings between the coal owners and miners representatives began again on 12 April 1921. The leaders of the “Triple Alliance” capitulated and the strike was called off on 15 April.