The Glorious First of June, also known as the Fourth Battle of Ushant, (known in France as the Bataille du 13 prairial an 2 or Combat de Prairial) was fought on 1 June 1794 between the British and French navies during the War of the First Coalition. It was the first and largest fleet action of the French Revolutionary Wars.

The action was the culmination of the Atlantic campaign of May 1794, which had criss-crossed the Bay of Biscay over the previous month and saw both sides capturing numerous merchant ships and small warships along with engaging in two partial, but inconclusive, fleet actions. The British Channel Squadron under Admiral Lord Howe attempted to prevent the passage of a vital French grain convoy from the United States, which was protected by the French Atlantic Squadron, commanded by Counter-admiral Louis Thomas Villaret de Joyeuse. The two forces clashed in the Atlantic Ocean, some 400 nautical miles (700 km) west of the French island of Ushant on 1 June 1794.

During the battle, Howe defied naval convention by ordering his fleet to turn towards the French and for each of his vessels to rake and engage their immediate opponent. This unexpected order was not understood by all of his captains, and as a result, his attack was more piecemeal than he intended. Nevertheless, his ships inflicted a severe tactical defeat on the French fleet. In the aftermath of the battle both fleets were left shattered; in no condition for further combat, Howe and Villaret returned to their home ports. Despite losing seven of his ships of the line, Villaret had bought enough time for the French grain convoy to reach safety unimpeded by Howe's fleet, securing a strategic success. However, he was also forced to withdraw his battle fleet back to port, leaving the British free to conduct a campaign of blockade for the remainder of the war. In the immediate aftermath, both sides claimed victory and the outcome of the battle was seized upon by the press of both nations as a demonstration of the prowess and bravery of their respective navies.

The battle demonstrated a number of the major problems inherent in the French and British navies at the start of the French Revolutionary Wars. Both admirals were faced with disobedience from their captains, along with ill-discipline and poor training among their shorthanded crews, and they failed to control their fleets effectively during the height of the combat.

Since early 1792 France had been at war with four of its neighbours on two fronts, battling the Habsburg monarchy and Prussia in the Austrian Netherlands, and the Austrians and Piedmontese in Italy. On 2 January 1793, almost one year into the French Revolutionary War, republican-held forts at Brest in Brittany fired on the British brig HMS Childers. A few weeks later, following the execution of the imprisoned King Louis XVI, diplomatic ties between Britain and France were broken. On 1 February, France declared war on both Britain and the Dutch Republic.

Protected from immediate invasion by the English Channel, Britain prepared for an extensive naval campaign and dispatched troops to the Netherlands for service against the French. Throughout the remainder of 1793, the British and French navies undertook minor operations in Northern waters, the Mediterranean and the West and East Indies, where both nations maintained colonies. The closest the British Channel Squadron had come to an engagement was when it had narrowly missed intercepting the French convoy from the Caribbean, escorted by 15 ships of the line on 2 August. The only major clash was the Siege of Toulon, a confused and bloody affair in which the British force holding the town—alongside Spanish, Sardinian, Austrian and French Royalist troops—had to be evacuated by the Royal Navy to prevent its imminent defeat at the hands of the French Revolutionary Army. The aftermath of this siege was punctuated by recriminations and accusations of cowardice and betrayal among the allies, eventually resulting in Spain switching allegiance with the signing of the Treaty of San Ildefonso two years later. Nevertheless, the siege produced one major success: Sir Sidney Smith, with parties of sailors from the retreating British fleet, accomplished the destruction of substantial French naval stores and shipping in Toulon. More might have been achieved had the Spanish raiding parties that accompanied Smith not been issued with secret orders to stall the destruction of the French fleet.

The situation in Europe remained volatile into 1794. Off northern France, the French Atlantic Squadron had mutinied due to errors in provisions and pay. In consequence, the French Navy officer corps suffered greatly from the effects of the Reign of Terror, with many experienced sailors being executed, imprisoned or dismissed from the service for perceived disloyalty. The shortage of provisions was more than a navy problem though; France itself was starving because the social upheavals of the previous year had combined with a harsh winter to ruin the harvest. By this time at war with all her neighbours, France had nowhere to turn for overland imports of fresh provisions. Eventually a solution to the food crisis was agreed by the National Convention: food produced in France's overseas colonies would be concentrated on board a fleet of merchant ships gathered in Chesapeake Bay, and augmented with food and goods purchased from the United States. During April and May 1794, the merchantmen would convoy the supplies across the Atlantic to Brest, protected by elements of the Atlantic Squadron.

The navies of Britain and France in 1794 were at very different stages of development. Although the British fleet was numerically superior, the French ships were larger (even if more lightly built), and carried a heavier weight of shot. The largest French ships were three-decker first rates, carrying 110 or 120 guns, against 100 guns on the largest British vessels.