At 2115 on 6 December the 1st Marine Division requested by dispatch that the relief be completed the next day in order to free 1/1 for the attack to the north. The relief column, designated Task Force Dog and commanded by Brigadier General Armistead D. Mead, ADC of the 3d Infantry Division, consisted of the 3d Battalion, 7th Infantry, the 92d Armored Field Artillery Battalion, plus detachments of engineers, signalmen, and antiaircraft troops. Brushing aside some Chinese roadblocks, it arrived at Chinhung-ni on the afternoon of the 7th and relieved 1/1 immediately.[584] [584] Smith, _Notes_, 1063–1064; X Corps _Special Report, Chosin Reservoir_, 20–24; X Corps _OI 26_, 5 Dec 50; and Dolcater, _3d Infantry Division in Korea_, 90; CG 1stMarDiv msg to CG X Corps, 2115 6 Dec 50; CG X Corps msg X 13811, 7 Dec 50; Col D. M. Schmuck Comments, n. d. _Air Drop of Bridge Sections_ Another problem which the 1st Marine Division planners had faced at Hagaru called for an engineering solution. As early as 4 December the commanding general was notified that a critical bridge three and a half miles south of Koto-ri (see Map 29) had been blown by the enemy for the third time. At this point water from the Chosin Reservoir was discharged from a tunnel into four penstocks, or large steel pipes, which descended sharply down the mountainside to the turbines of the power plant in the valley below. Where the pipes crossed the road, they were covered on the uphill side by a concrete gatehouse, without a floor. On the downhill side was the one-way bridge over the penstocks which the enemy had thrice destroyed. Between the cliff and the sheer drop down the mountainside there was no possibility of a bypass. Thus the gap of 16 feet (24 feet, counting the abutments) must be spanned if the Division was to bring out its vehicles, tanks and guns.[585] [585] Except when otherwise specified, this section is based on the following sources: Partridge interv, 25 Jun 51, 48–63; Litzenberg interv, 27–30 Apr and 15 Jul 51, 72–73; Smith, _Notes_, 1057–1059, 1075, 1095–1109; 1stEngBn _SAR_, 3–14; Geer, _The New Breed_, 361–362, 369; LtCol J. H. Partridge Comments, n. d.