 Following Soult 's appropriation of many of Victor 's troops , the Allies sensed an opportunity to engage Marshal Victor in open battle and raise the siege of Cádiz . To that end , an Anglo @-@ Spanish expedition was sent by sea from Cádiz south to Tarifa , with the intention of marching north to engage the French rear . This force comprised some 8 @,@ 000 Spanish and 4 @,@ 000 British troops , with the overall command ceded to the Spanish General Manuel la Peña , a political accommodation since he was widely regarded as incompetent . To coincide with la Peña 's assault , it was arranged that General José Pascual de Zayas y Chacón would lead a force of 4 @,@ 000 Spanish troops in a sally from Cádiz , via a pontoon bridge from the Isla de León . 
