From their formal organisation as Trained Bands in 1572 they defended the coastline, watched the Spanish Armada and took an active part in the English Civil War.
After a long hiatus, the Sussex Militia was reformed in 1778 and provided internal security and home defence in all of Britain's major wars thereafter.
After the Cardwell Reforms the RSLIM became a battalion of the Royal Sussex Regiment and saw active service in the Second Boer War.
The English militia was descended from the Anglo-Saxon Fyrd, the military force raised from the freemen of the shires under command of their Sheriff.
The coastal towns of Sussex forming part of the Cinque Ports also had a legal obligation to supply ships, seamen and marines for the Royal Navy.
They were mustered in April when the returns from Sussex indicated that of 7572 able-bodied men in the county 2004 were trained, and a further 2001 were armed but untrained, in addition to the cavalry:[23]
[28][30] Control of the trained bands was one of the major points of dispute between Charles I and Parliament that led to the English Civil War.
However, with a few exceptions neither side made much use of the trained bands during the war beyond securing the county armouries for their own full-time troops.
[26][31] Sussex was one exception, its TBs seeing some action, first when involved in the siege of Portsmouth and Southsea Castle when they were captured for Parliament by Sir William Waller in September 1642.
[28][32] On the night of 15 November a group of Royalists in Chichester overpowered Captain Henry Chitty's company of trained bandsmen guarding the walls and seized their cannon at the North Gate (one of those captured at Portsmouth).
Chitty and William Cawley, the Member of Parliament (MP) for Midhurst, fled to Portsmouth while the Royalists secured the trained band armoury.
Next day the Royalist High Sheriff of Sussex, Sir Edward Ford, arrived with a force to garrison Chichester.
Morley then gathered additional volunteers and recaptured Arundel, afterwards joining Waller, whose army retook Chichester in December 1642.
[28][32][33][34][35] A year later, in December 1643, Lord Hopton captured Arundel Castle for the Royalists once more, when Catcott's Company of the Sussex TBs was in the garrison.
Under the Commonwealth and Protectorate the militia received pay when called out, and operated alongside the New Model Army to control the country.
Sussex was given a quota of 800 men to raise, but failed to do so – possibly because the Leader of the Opposition, the Duke of Newcastle, and his Pelham family members were powerful in the county.
Newcastle had opposed the Militia Acts, but even he felt that Sussex, a county standing right in the path of potential invasion, should raise its men.
It was raised and embodied at Chichester on 29 June 1778, the Lord Lieutenant of Sussex, Charles Lennox, 3rd Duke of Richmond, taking personal command as colonel.
The force was still unpopular in Sussex: the imposition of the Militia Ballot caused riots in the county, but the officers took over from the parish constables the task of raising subscriptions from those who were liable, and used the money to hire volunteers.
[55] From 1784 to 1792 the militia were assembled for their 28 days' annual peacetime training, but to save money only two-thirds of the men were actually mustered each year.
These were mustered on 29 March 1797 for 20 days' training, with three companies at Chichester, two at Arundel, two at Shoreham-by-Sea, one at East Grinstead, three at Horsham and three at Lewes.
These were raised to counter the declining numbers of Volunteers, and if their ranks could not be filled voluntarily the Militia Ballot was employed.
[69][70] From November 1813 the militia were invited to volunteer for limited overseas service, primarily for garrison duties in Europe.
Although officers continued to be commissioned into the militia and ballots were still held, the regiments were rarely assembled for training and the permanent staffs of sergeants and drummers were progressively reduced.
Their role was to man coastal defences and fortifications, relieving the Royal Artillery (RA) for active service.
[73][79][80][81] War having broken out with Russia in 1854 and an expeditionary force sent to the Crimea, the militia began to be called out for home defence.
The Militia Reserve introduced in 1867 consisted of present and former militiamen who undertook to serve overseas in case of war.
[74] Under the 'Localisation of the Forces' scheme introduced by the Cardwell Reforms of 1872, the militia were brigaded with their local Regular and Volunteer battalions.
The militia now came under the War Office rather than their county lords lieutenant and battalions had a large cadre of permanent staff (about 30).
[55][94][95] Its role throughout the war was to prepare reinforcement drafts of reservists, special reservists, recruits and returning wounded for the regular battalions serving overseas: the 1st Royal Sussex remained in India throughout the war, but the 2nd Bn went to France with the British Expeditionary Force and fought on the Western Front until the Armistice with Germany.