What was not known, however, was the extent of these subterranean shelters. One Chinese account, allegedly written by a reconnaissance staff officer named Li Yo-Yang, described the protection of a CCF shelter to a recently captured UN prisoner as they were under Allied artillery bombardment. While shells exploded all around the position the enemy boasted: “There’s no danger of being killed on a position fortified by the Chinese People’s Volunteers.... Don’t you know it’s impossible for your shells to penetrate our air-raid shelters?”[166] An American report on enemy field fortifications estimated that the amount of earth cover in Chinese air-raid shelters was as high as 20 feet, and in frontline defensive positions, up to 33 feet.[167] [166] _A Volunteer Soldier’s Day: Recollections by Men of the Chinese People’s Volunteers in the War to Resist U.S. Aggression and Aid Korea_ (Peking: Foreign Languages Press, 1961), p. 193, hereafter CPV, _Recollections_. [167] _PacFlt EvalRpt_ No. 5, p. 8-90. Marine defensive installations carved out of the ground were not so extensive as those of the enemy opposing JAMESTOWN. “In spite of orders, instructions, and inspections many bunkers were only half dug in, then built up above the ground with sandbags,” observed one Marine battalion commander.[168] Back in April, just after the Marine division had settled in the west, its 1st Engineer Battalion, using U.S. Army drawings, had published bunker construction plans. Express instructions to frontline units were to “construct bunkers to provide simultaneously living and fighting space. Overhead cover on all bunkers will be such as to withstand direct hit from 105mm and to allow friendly VT fire over position.”[169] [168] LtCol Roy J. Batterton, Jr., “Random Notes on Korea,” _Marine Corps Gazette_, v. 39, no. 11 (Nov 55), p. 29, hereafter Batterton, _Korea Notes_. [169] CO 5thMar msg to 5thMar units, dtd 20 Apr 52, in 5thMar ComdD, Apr 52, #2, App. II, p. 6. Some officers felt it was, perhaps, the work-during-light, patrol-at-night routine that resulted in the shallow draft Marine bunkers. Others suggested that the relatively limited defensive training received by the more offensive-minded Marines created a natural apathy to digging elaborate fighting positions.