Hamhung straddles the main railroad connecting Wonsan and Sonjin as it follows the coastal route to the border of Soviet Russia. A narrow-gauge line (2′ 6″) stems from Hungnam and passes through Hamhung before penetrating into the mountainous heart of North Korea. Parallel to this railroad is the only highway that could be utilized by the transport of the 1st Marine Division for its advance to the north.
The MSR from Hungnam to Yudam-ni
Soon the eyes of the world would be fixed on maps of the narrow, winding 78-mile stretch of dirt and gravel road leading from the supply port of Hungnam to the forlorn village of Yudam-ni at the western tip of the Chosin Reservoir. Distances in road miles between points along the route are as follows:
| Hungnam to Hamhung | 8 |
| Hamhung to Oro-ri | 8 |
| Oro-ri to Majon-dong | 14 |
| Majon-dong to Sudong | 7 |
| Sudong to Chinhung-ni | 6 |
| Chinhung-ni to Koto-ri | 10 |
| Koto-ri to Hagaru | 11 |
| Hagaru to Yudam-ni | 14 |
| 78 |
The first half of the distance—the 43 miles from Hungnam to Chinhung-ni—is traversed by a two-lane road passing through comparatively level terrain. Rolling country is encountered north of Majon-dong, but it is at Chinhung-ni that the road makes its abrupt climb into a tumbled region of mile-high peaks. There are few straight or level stretches all the rest of the 35 miles to Yudam-ni, but the route from Chinhung-ni to Koto-ri is the most difficult.
Funchilin Pass, comprising eight of these ten miles, represents an ascent of 2500 feet for a straining jeep or truck. The road is merely a twisting, one-way shelf, with a cliff on one side and a chasm on the other.
About two miles south of Koto-ri the trail reaches a rugged plateau region. There it rejoins the railway along the Changjin River, though the narrow-gauge line was operative only from Hamhung to Chinhung-ni.
Hagaru, at the southern tip of the Chosin Reservoir, with highways branching off on both sides of that body of water, was an important communications center before the war. And even though many buildings had been flattened by bombing, the town was still impressive as compared to such wretched mountain hamlets as Koto-ri and Chinhung-ri.
The road from Hagaru to Yudam-ni climbs from the tableland at the foot of the Chosin Reservoir and winds its way up to 4000-foot Toktong Pass. Descending through gloomy gorges, it finally reaches a broad valley leading to Yudam-ni, where roads branch off to the north, west, and south from a western arm of the Reservoir.
This was the 78-mile main supply route that would soon be claiming its page in history. In only a few weeks it would be known to thousands of Marines as the MSR, as if there never had been another.