Although the unit saw no active service, it supplied trained gunners to siege batteries engaged on the Western Front during World War I.

[1][2] However, two years later the two Sussex companies were split off to form a separate Sussex Royal Garrison Artillery with the following organisation:[2][3][4] The unit was responsible for the defended port of Newhaven in South Eastern Coast Defences, which was guarded by two 6-inch Mk VII guns mounted at Newhaven Fort.

[9][10] By October 1914, the campaign on the Western Front was bogging down into Trench warfare and there was an urgent need for batteries of siege artillery to be sent to France.

[12][13] This process meant a continual drain on the manpower of the defended ports units and in April 1917, the coastal defence companies of the RGA (TF) were reorganised.

[3][17] The battery landed in France on 1 April 1916 equipped with four 9.2-inch howitzers and joined 27th Heavy Artillery Group (HAG) supporting III Corps in Fourth Army.

[17][18][19] Fourth Army was preparing for that year's 'Big Push', the Battle of the Somme, with III Corps facing the German redoubts in front of Ovillers.

[18][19][27][28][29] 69th Siege Bty was next sent to rejoin Fourth Army, which had assembled round Nieuport to carry out a planned attack along the Belgian coast in support of the Flanders Offensive.

British preparations were disrupted by a German spoiling attack and there was no breakthrough at Ypres so Fourth Army's operation was cancelled.

Over the following weeks the British batteries exchanged CB fire with their German opposite numbers, with numerous casualties to gunners and guns.

[12][18][32] On 28 March the German Spring Offensive extended to First Army's front (the Third Battle of Arras), beginning with a massive bombardment.

69th Siege Bty was subjected to a barrage of high explosive (HE) and gas shells and suffered heavy casualties, including the officer commanding, Maj Cyril Scholefield, who was killed.

By early September hostile shelling was well below normal levels, and as the enemy pulled back out of range 83rd Bde's batteries were placed in GHQ Reserve.

The guns then moved up to support the successful surprise attack of the Battle of Épehy (18 September), when the massed artillery crushed a German counter-attack.

46th (NM) Division swarmed over the canal across captured bridges and dams, using lifebelts and planks, and took its final objectives before nightfall.

Next morning the brigade put down heavy barrages in front of a renewed attack, after which the Germans retired across the Sambre–Oise Canal and destroyed the bridges behind them.

In mid-September 8 HAG was ordered to move south with its batteries to join VII Corps where it was engaged in CB tasks supporting the adjacent Reserve Army attacking on the Somme.

The battery's observation post (OP) in the front line was overrun by German infantry appearing out of the morning fog.

The rest of the battery fired most to delay the enemy crossing their bridgehead at Moÿ-de-l'Aisne but later was almost surrounded by German infantry who had broken through 14th Division's positions.

The Battery Sergeant Major, with a few gunners, manned the anti-aircraft Lewis guns to defend the position while the howitzers fired over open sights.

[63] Here 66th Bde re-assembled and was re-equipped; it was ready for action again on 19 April under VI Corps and spent the next three months exchanging fire with hostile batteries and engaging in HF tasks.

In late August, with the Allied Hundred Days Offensive under way, 66th Bde moved up to Arras to support Third Army's attacks at the Scarpe and the Drocourt-Quéant Switch Line.

During the Battle of the Selle on 20 October the battery was supporting the attack on the high ground east of Haussy when a single high-velocity shell killed six men and wounded another 16.

[12] When the TF was reconstituted on 7 February 1920 the Sussex RGA was reformed from No 2 Company with HQ and one battery, based at the Drill Hall, Watergate Lane, Lewes.

The TF was reorganised as the Territorial Army (TA) in 1921, when the unit was redesignated as the Sussex Coast Brigade, RGA and the battery was designated 159 Bty.