here is what the official historian of the US Army says about the subject. from:
CCF IN ATTACK
Toward a clearer understanding of what shall be said hereinafter as to weapons effects and tactical arrangements within the Eighth Army, one particular point concerning CCF characteristics in the attack and on defense requires clarification.
The word "mass" has been used quite loosely in descriptions of enemy operations circulated in this country. Press accounts have given the impression that the Chinese attack in great numbers closely concentrated. Some official documents have also used the term rather indiscriminately, thus furthering the belief that broad targets are frequently presented to all weapons. There have been some targets of this character. For example, in the assault against 23rd Infantry Regiment positions in Chipyong-ni in early February, CCF pressed forward in fairly solid ranks, and were cut down in large numbers within small areas.
But intense concentrations are the exception. The Chinese do not characteristically employ mass, for example, in the way that the Red Army used it against the Germans in operations in the Ukraine during World War II, coming on in such numbers that the human sea absorbed and ultimately smothered the fire volume. Rather, in the attack, CCF tend to move against our works in multiple, thin lines, well spaced each from the other, after having deployed out of column in the last phase of the approach.
The approach column may be single file, or even a regiment moving four abreast, depending on the situation and the size of the attack force.
The nature of the ground also compounds the fire problem, since it induces greater dispersion. The ridges are not evenly bottomed or sided. There are frequent bulges,
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outcroppings, draws, and small ravines. In consequence, even when the attacking line advances quite uniformly, no defending weapon is likely to have a clear field of fire against any significant number of the enemy. When brought in check by the counter fire of various weapons, the enemy gradually presses forward against the position, but still does not tend to bunch excessively.
On defense, CCF make efficient employment of ground cover, eschew use of long intrenchments and tight formations, and in general so dispose themselves that our fires, in any type, rarely have a large killing opportunity. The chief effects are therefore achieved through the systematic employment of fires in combination, with no one weapon or group of weapons (such as mortars, artillery, or small arms) predominating in the delivery of decisive fire."