The 1st Royal Naval Brigade was an infantry brigade of the Royal Navy which was formed from excess naval reserve personnel. The brigade was formed in August 1914 and assigned to the 63rd (Royal Naval) Division after that division's formation in September 1914 and served on the Western Front and during the Gallipoli campaign, until July 1916 when it was broken up. The brigade was formed once more for a few days, but once again disbanded following the division's absorption into the Army's order of battle.

Before the beginning of the First World War, plans for a 'naval land force' were drawn up on the recommendation of the Committee for Imperial Defence: "[in the event of war] a force of Royal Marines would be formed under the control of the Admiralty, to be known as the 'Advanced Base Force'". When war was declared, this project was put into operation, and a brigade of marines, known as the Royal Marine Brigade (later the 3rd (Royal Marine) Brigade) was established with its administrative headquarters based in London.

By the time of mobilisation, the British Army could only muster six infantry divisions (of regulars) and two cavalry divisions. To meet this shortfall, troops were withdrawn from overseas postings and the Dominions as reinforcements for the expeditionary force sent to France. New volunteer units were also formed and trained, such as the local 'Pals battalions'. However, a new division of naval reservists and Marines surplus to the fleet would undoubtedly be a great help, with Herbert Kitchener, 1st Earl Kitchener, stating during a meeting of the House of Lords that "... Their presence in the field will be very welcome, for their fighting qualities are well known.".

In August 1914, as part of the mobilisation of the British Armed Forces following the German invasion of Belgium, the Royal Navy and Royal Marines Light Infantry, were organised into battalions and 'divisions'. These forces were organised along the same lines as their counterparts in the army, except for small details such as the rank of the commanding officer, and lack of bands, etc. The forces on long being organised into battalions were now organised into eight battalions, along with an artillery battalion and five battalions belonging to the Royal Marines, but were still sitting idly by. In addition, large numbers of naval reservists were available and much above those required for manning the fleet, so on 16 August 1914, the Admiralty decided to form two naval brigades, which were grouped with the Royal Marine Brigade into the 'Royal Naval Division'. The new division maintained an administrative headquarters at the Admiralty Building, but no operational headquarters was established until late August, after which it was based in Dover.

In accordance with the expansion of the battalions, 1st Naval Brigade, was established on 20 August 1914 at the Plymouth Naval Base. The new brigade was initially organised with four battalions from local naval stations and ships, and named after according to where the majority of its personnel came from. Each was to comprise four battalions, each of 880 men and to be organised in 16 'double companies' of 220 men.

The initial organisation, however, proved to be unmanageable, and each battalion was reorganised into the following structure: 28 x Petty Officers from the Royal Navy, 48 x Petty Officers from the Royal Fleet Reserve, 424 x Petty Officers, Leading Seamen, and Seamen from the Royal Naval Volunteer Reserve, 250 x 'Stokers' from the Royal Fleet Reserve, and 187 x Seamen under 30 years old from the Royal Naval Reserve. This left each battalion with personnel coming from across the navy, leaving a total of 937 sailors.

Because of the quick formation of the naval brigades, a new camp ground was hastily constructed from 700 tents to supplement the 170 marine tents already at hand in Deal in Kent. Sailors from the Royal Naval Volunteer Reserve were instructed to bring their own rifles, while arrangements were made to issue 4,000 rifles for the Royal Naval Reserve and Royal Fleet Reserve. These were of the old Lee–Enfield Bolt-action rifles, but orders were placed for the newer short type to be delivered at the earliest possible moment. Vickers received an order for 40 Maxim Machine-Guns, to be ready in 10 days; four would be issued to each battalion, with four kept in reserve. Each company therefore continued a machine-gun section, and each of the three brigades was to form a field ambulance column.

On 4 October 1914, the two newly formed naval brigades received orders to embark at the Port of Dover for a move to France. On the morning of 5 October, the brigades arrived in Dunkirk. The brigade was embarked once more onboard two troop trains, and a shore train, arriving in Antwerp, Belgium at 02:30 in the morning on 6 October. Immediately upon arrival the brigade joined the Royal Marine Brigade at the Antwerp defensive line. The Siege of Antwerp had been raging since 28 September, and by 6 October the Belgian garrison was close to surrender. During the afternoon of the 6th, the brigade was detached to the right flank of the Royal Marine Brigade. This position however, was seen as untenable and during the night of 6–7 October, the (now organised) Royal Naval Division withdrew and occupied the 2nd line of trenches. The 1st Naval Brigade was dug in around the positions of Forts No. 1-8, with brigade holding the far left flank.