Operation AMAZON, published by I Corps on 12 June, ordered that bridging preparations be made for the approaching summer flood season. The previous August at the Honker Bridge, the one nearest the railhead, the Imjin had crested some 27 feet above normal. One reason for the precautionary efforts taken to insure bridge security during the flood season was the potential damage the Chinese could cause. Since they controlled the upriver area of the Imjin, before it entered the division sector, they could introduce floatable debris or explosives into the swift running flood waters. Another major concern was the logistical problem that would be faced by forward MLR units in event the bridges became impassable and the enormous strain that would thus be placed on helicopter resupply operations. The I Corps directive specified that its divisions maintain a transport capability that would enable medium tanks to pass safely over bridges spanning the major rivers in their I Corps sector. The order also called for the removal of debris that could cause damage to bridges. Removal of those bridges vulnerable to flood conditions and the erection of emergency river spans were also to take place on corps order. To carry out the I Corps operational order, General Seiden put the division’s own AMAZON plan into effect on 1 July. On this date Companies A, B, and D of Lieutenant Colonel Harry D. Clarke’s 1st Engineer Battalion began extensive preparations for debris removal from the four bridge sites in the division sector. Even before this, Marine engineers and shore party personnel had been trained at special schools to handle U.S. Army equipment provided for the AMAZON operation.[156] [156] This included employment of the 60-inch searchlight for night illumination, maintenance of boats for debris removal, and operation of the M-4 ferry. Other preparations by the division, of a non-engineer nature, included positioning of 13,000 life-saving floatation devices for use by frontline troops should they become shut off from planned evacuation. Beginning 1 June, division engineers began blasting away at objects that flood waters could loosen and carry into the bridge supports. Bridge approaches were improved and their supports strengthened. Each company had a detail living at the bridge site for which it was responsible. With the advent of heavy rains, these Marines were to operate 24-hour boat patrols to keep the river free of debris. The engineers were also to maintain a round-the-clock debris watch at the four division bridges--Freedom Gate, or the Munsan-ni Railroad Bridge in the left regimental sector; Honker and X-Ray in the center; and finally, Widgeon, very close to the Commonwealth boundary.