The main landing of Japanese forces targeted Lingayen Gulf, with its proximity to the Philippine capital of Manila, and Lamon Bay on the opposite coast to the south.

The force contained the IJA 48th Division (less the Tanaka and Kanno Detachments which had already landed in the invasions of Aparri and Vigan) under Lt General Yuitsu Tsuchihashi.

The Takao convoy was scheduled to land at Agoo, a small village in La Union Province on the eastern shore of Lingayen Gulf beginning 0500 on 22 December.

The Kamijima Detachment in particular was to strike north to occupy San Fernando, and Baguio and to consolidate with the Vigan invasion force under Colonel Tanaka which was moving south along the coast.

Lingayen Gulf was the most logical site for a large invasion force to land, but the entire 120 mile coast was protected by only two Philippine Commonwealth Army divisions, of which only one had any artillery.

The only location where the Japanese faced ground opposition was at Bauang, where the Philippine 12 Infantry HQ Battalion opened fire with its one 50-caliber machine gun on the Kamijima Detachment as it landed.

However, the Japanese advance was too quick for the inexperienced and poor-trained Philippine troops to get into position, and Bonnett subsequently gave orders for the division to withdraw to beyond Baguio by midnight.

In the southern sector of the front, the Japanese 1st Formosa and a portion of the 48th Mountain Artillery battalions under the command of Colonel Hifumi Imai landed at Aringay by 1030 and advanced south towards Rosario along the coastal road.

The 48th Division was ordered to take the town of San Fabian, which had two 155-mm coastal artillery guns, and the Japanese drive along the Lingayen coastline was accordingly extended further south than originally planned.

When the 26th Cavalry encountered forward elements of the Japanese 48th Reconnaissance and 4th Tank Regiments, it fell back to the hamlet of Damoritis, where defensive positions had been established.

Earlier in the afternoon, Wainwright had ordered Brig General Clyde A. Selleck to take the Philippine 71st Division to Damortis to hold the junction of the Rosario-Baguio road east of Rosario.

On the morning of 23 December, the Philippine 71st Division set up defensive positions along Route 3 south of Sison, with the remnants of the 26th Cavalry falling back to Pozorrubio to reorganize.

Even before the fall of Sison, Wainwright had received permission from General MacArthur to withdraw behind the Agno River as he believed that further defense of the Lingayen area was impossible.

Despite adverse weather, General Homma was able to land the bulk of his forces at Lingayen Gulf with little opposition, and in a matter of a few days had secured the northern approaches to the Philippine capital of Manila.