On 16 June 1779, the Spanish issued what was in effect a declaration of war against Great Britain, and a blockade immediately commenced. On 6 July 1779, an engagement took place between the British ships and Spanish vessels bringing supplies to the Spanish troops on shore. Several Spanish vessels were taken and the hostilities began. The combined Spanish and French fleets blockaded Gibraltar from the sea, while on the land side an enormous army constructed forts, redoubts, entrenchments, and batteries from which to attack.