The 14th Regiment, 6th Division, turned over the Ongjin Peninsula area to security forces of the BC 3rd Brigade on the second day and immediately departed by way of Haeju and Kaesong to rejoin its division. [03-18]
June 25, 1950
The invasion began in the west, on the Ongjin Peninsula.
Scattered but heavy rains fell along the 38th Parallel in the pre-dawn darkness of Sunday, 25 June 1950. Farther south, at Sŏul, the day dawned overcast but with only light occasional showers. The summer monsoon season had just begun. Rain-heavy rain-might be expected to sweep over the variously tinted green of the rice paddies and the barren gray-brown mountain slopes of South Korea during the coming weeks.
Along the dark, rain-soaked Parallel, North Korean artillery and mortars broke the early morning stillness. It was about 0400. The precise moment of opening enemy fire varied perhaps as much as an hour at different points across the width of the peninsula, but everywhere it signaled a coordinated attack from coast to coast. The sequence of attack seemed to progress from west to east, with the earliest attack striking the Ongjin Peninsula at approximately 0400. [03-9] (Map 1)
The blow fell unexpectedly on the South Koreans. Many of the officers and some men, as well as many of the KMAG advisers, were in Sŏul and other towns on weekend passes. [03-10]
The four NKPA divisions were attacking four ROK battalions. And even though four divisions and one regiment were stationed near the border, only one regiment of each division and one battalion of the separate regiment were actually in the defensive positions at the Parallel. The remainder of these organizations were in reserve positions ten to thirty miles below the Parallel. Accordingly, the onslaught of the North Korea People's Army struck a surprised garrison in thinly held defensive positions.
June 25, 0600
The first message from the vicinity of the Parallel received by the American Advisory Group in Sŏul came by radio about 0600 from five advisers with the ROK 17th Regiment on the Ongjin Peninsula. They reported the regiment was under heavy attack and about to be overrun.
June 25, 0600
When Paik began issuing orders, his three regiments were disposed as follows.
The 12th was at the parallel near Kaesŏng, outflanked by the train borne NKPA soldiers and apparently overrun.
The 13th was about fifteen miles east of Kaesŏng [near Korangp'o-ri] and
the 11th was in reserve near Sŏul.
[The 11th Regiment moved rapidly and in good order from Suisak and took position on the left of the 13th Regiment]
Paik ordered the 11th to move rapidly forward to positions behind the Imjin River. For the next two days the 11th and 13th ROK regiments would fight valiantly at the Imjin in a vain attempt to hold back nearly two full NKPA divisions, whose attack was led by a battalion of T-34 Russian tanks.[2-79]
This NKPA attack was powerful and determined, but the main attack came as expected, in the Uijŏngbu Corridor. Two full NKPA divisions, each spearheaded by forty T34 tanks and other mechanized vehicles and supported by 120mm howitzers, hit the ROK 7th Division. The ROKs reeled, recovered, then mounted a surprisingly stout defense.
As planned, Sŏul ordered the 2nd Division to move rapidly forward from Taejŏn to reinforce this critical corridor. But the 2nd could not get there in time. The 7th was forced to give way. It fell back on Uijŏngbu, thereby exposing the right flank of Paik's 1st Division, which was holding along the Imjin River, and forcing Paik to fall back toward Sŏul. [not for two days, I hope]
Farther east, in the hills of mid-Korea, elements of two other NKPA divisions simultaneously struck the ROK 6th Division. As with Paik's 1st, only two regiments were on the line; but as it happened, he had not issued any weekend passes, and these regiments were at full strength. Besides that, the ROK 6th Division had unusually good artillery units. Its forward elements, some fighting from concrete pillboxes, held, giving the commanders time to rush the reserve regiment forward from Wŏnju, forty miles south. The division inflicted harsh casualties on the NKPA regiments and might have held longer, but the collapse of the ROK 7th Division at Uijŏngbu exposed its distant left flank, also forcing it to withdraw.
There were two other subsidiary D day NKPA attacks on the extreme flanks.
West of Paik's 1st Division, on the Ongjin peninsula, which juts into the Yellow Sea, a strong NKPA force attacked the lone 17th ROK Regiment, commanded by Paik's younger brother. One ROK battalion was overrun and decimated, but the other two evacuated as planned (the ROKs correctly did not consider the peninsula defensible) on three LST's.
On the opposite side of Korea, on the mountainous east coast bordering the Sea of Japan, the NKPA simultaneously hit the widely dispersed and under strength ROK 8th Division, both frontally and by multiple amphibious assaults on its coastal flanks. Caught in a well executed land-sea envelopment, the division was powerless to mount an effective defense, and was soon forced to withdraw.
During these well planned and well executed quadruple assaults the NKPA Air Force was out in full force, about 100 planes. Some of the bombers attacked Sŏul and its airport, Kimp'o, causing panic among the civilians. Some of the fighters bombed and strafed ROK Army forces. But the NKPA Air Force's contribution to the battle was slight. Contrary to the predictions of Roberts and Muccio, the ROK soldiers did not panic; they all but ignored the planes. Of far greater menace and effectiveness were the Russian T34 tanks. The NKPA made a mockery of Roberts's judgment that Korea was "not good tank country." The T34s rolled southward, easily and relentlessly, creating terror and panic among most ROK units. But not all. About ninety of Paik's 1st Division troopers died valiantly in suicidal attempts to destroy the tanks with satchel charges and other makeshift explosive devices.
June 25, 1950 0900
The North Korean attack against the Ongjin Peninsula on the west coast, northwest of Sŏul, began about 0400 with a heavy artillery and mortar barrage and small arms fire delivered by the NKPA 14th Regiment of the NKPA 6th Division and the BC 3rd Brigade. The ground attack came half an hour later across the Parallel without armored support. It struck the positions held by a battalion of the ROK 17th Regiment commanded by Col. Paik In Yup. 
The first message from the vicinity of the Parallel received by the American Advisory Group in Sŏul came by radio about 0600 from five advisers with the ROK 17th Regiment on the Ongjin Peninsula. They reported the regiment was under heavy attack and about to be overrun. 
Before 0900 another message came from them requesting air evacuation. Two KMAG aviators, Maj. Lloyd Swink and Lt. Frank Brown, volunteered to fly their L-5 planes from Sŏul. They succeeded in bringing the five Americans out in a single trip. [03-16]
The Ongjin Peninsula, cut off by water from the rest of South Korea, never had been considered defensible in case of a North Korean attack. Before the day ended, plans previously made were executed to evacuate the ROK 17th Regiment. What was left, 2 battalions.
June 25, 1950 1235
Shortly after noon, at 1235, Premier Kim Il Sung, of North Korea, claimed in a radio broadcast that South Korea had rejected every North Korean proposal for peaceful unification, had attacked North Korea that morning in the area of Haeju above the Ongjin Peninsula, and would have to take the consequences of the North Korean counterattacks.
June 26, 1950
Two LST's from Inch'ŏn joined one already offshore, and on Monday, 26 June, they evacuated Col. Paik In Yup (17th Regiment, and most of two battalions-in all about 1,750 men. The other battalion was completely lost in the early fighting.
The 14th Regiment, 6th Division, turned over the Ongjin Peninsula area to security forces of the BC 3rd Brigade on the second day and immediately departed by way of Haeju and Kaesŏng to rejoin its division.
East of the Ongjin Peninsula, Kaesŏng, the ancient capital of Korea, lay two miles south of the Parallel on the main Sŏul-P'yŏngyang highway and railroad. Two battalions of the 12th Regiment, ROK 1st Division, held positions just north of the town. The other battalion of the regiment was at Yŏnan, the center of a rich rice-growing area some twenty miles westward.
The 13th Regiment held Korangp'o-ri, fifteen air miles east of Kaesŏng above the Imjin River, and the river crossing below the city. The 11th Regiment, of the 1st Division in reserve, and division headquarters were at Suisak, a small village and cantonment area a few miles north of Sŏul. Lt. Col. Lloyd H. Rockwell, senior adviser to the ROK 1st Division, and its youthful commander, Col. Paik Sun Yup, had decided some time earlier that the only defense line the division could hold in case of attack was south of the Imjin River.
Songak-san (Hill 475), a mountain shaped like a capital T with its stem running east-west, dominated Kaesŏng which lay two miles to the south of it. The 38th Parallel ran almost exactly along the crest of Songak-san, which the North Koreans had long since seized and fortified. In Kaesŏng the northbound main rail line linking Sŏul-P'yŏngyang-Manchuria turned west for six miles and then, short of the Yesŏng River, bent north again across the Parallel.