Despite heavy casualties of the past 2 months, NKPA overall strength was estimated as high as 133,000 men as the result of filling the ranks with hastily trained replacements. Thirteen infantry regiments, 3 security regiments and the remnants of the original 3 armored regiments were believed to be participating in the offensive.[329] [329] Maj H. D. Stewart, “Rise and Fall of an Army,” _Military Review_, 30, no. 11:32–35 (Feb 51). For 2 months the Eighth Army had been purchasing time with space, and the enemy realized that time was now fighting on the side of the United Nations. The first ground force unit sent by a member nation to reinforce United States and ROK troops was the British 27th Infantry Brigade, which landed and took over a sector early in September. But the enemy knew that other UN contingents had been promised. The reorganized ROK army, moreover, had recovered from its early disasters and was giving a good account of itself in the northern sectors of the Pusan Perimeter. There the 1st, 3d, 6th, 8th, and Capital Divisions had not only maintained their tactical integrity throughout August but even delivered several counterattacks.[330] [330] U. S. Dept of State, “Fifth Report to the Security Council, October 5, 1950,” _United Nations Action in Korea under Unified Command_ (Washington: GPO, 1950). The NKPA numerical superiority, in short, could not last much longer. It was now or never if the invaders hoped to batter their way to Pusan, and Pyongyang staked everything on a final offensive. The brunt fell upon the United States 2d Infantry Division. Troops from four enemy divisions were identified on this sensitive front, well supported by armor and artillery. Within a few hours pressure became so great that EUSAK decided to send the Marine mobile reserve to the aid of the Army troops. Not only was the terrain familiar to Marines who had fought their way up Obong-ni Ridge, but they were renewing acquaintance with the same enemy outfit. For G-2 reports confirmed that the NKPA 4th Infantry Division was back again at the old stand--or at least such survivors as had emerged with a whole skin from their defeat of 17–18 August in this area. Perhaps because of the large numbers of new recruits filling the ranks, the retreaded outfit followed in reserve just behind the NKPA 9th Infantry Division as it crossed the Naktong and drove eastward. The 9th was one of the enemy units hastily raised from constabulary forces for purposes of the invasion. Assigned to guard duty at Seoul throughout July and half of August, the troops devoted themselves wholeheartedly to the pleasant mission of forcing South Koreans to “volunteer” as soldiers or laborers against their own people. Thus the division could be considered a fresh and rested outfit, though deficient in training and combat discipline as compared to the older NKPA units.