On the 21st of July he left Guantanamo Bay and, taking the Spaniards as well as the War Department completely by surprise as to his point of attack, he effected a landing on the 26th at Guanica, near the southwestern corner of Porto Rico.
The expeditionary force to Porto Rico, however, consisted not of 30,000 men but of only about 15,000; and it was not fully assembled on the island until the 8th of August.

The total Spanish forces amounted to only about 10,000, collected on the defensible ground to the north and in the interior, so that they did not disturb the disembarkation.

The American Army which had been dispatched from large Atlantic ports, such as Charleston and Newport News, seems to have been better and more systematically equipped than the troops sent to Santiago.

The Americans occupied Guanica, Ponce, and Arroyo with little or no opposition, and were soon in possession of the southern shores of the island.
Between the American forces and the main body of the enemy stretched a range of mountains running east and west through the length of the island.

San Juan, the only fortress, which was the main objective of the American Army, lay on the opposite side of this mountain range, on the northern coast of the island.