Still another concept regarding the employment of artillery developed during the early days of the JAMESTOWN defense. The 11th Marines had advised the infantry regiments that it could effectively fire on enemy troops attacking friendly positions if the Marines had overhead cover. The idea was to use variable time (VT) fuzes[119] with the standard high explosive (HE) shells. Artillery battalions supporting the frontline regiments registered on positions occupied frequently by patrols going forward from JAMESTOWN. [119] A type of proximity fuze, the V.T. depends upon an external source, such as an electronic signal, rather than the force of ground impact, to detonate the shell at a predetermined height over the target. According to the recollections of veteran artillery and infantrymen in the division, the first occasion that pre-planned artillery fire was placed on friendly positions occurred in May 1952.[120] The episode involved a 2/7 platoon patrol that late on 18 May was ordered to return to the MLR from an outpost on the former OPLR. Operating forward of the center regimental sector,[121] the platoon commander, Second Lieutenant Theodore H. Watson, directed that two of the three Marine squads return to the MLR. The remaining unit, surrounded by about 50 Chinese, engaged them in a brisk fire fight. [120] 1stMarDiv ComdD, May 52, p. 4. [121] The 7th Marines advanced to the line to relieve the 5th Marines in the center sector on 11 May. When the artillery fired to seal off the enemy and box-in the defensive position failed to discourage the hostile force, Lieutenant Watson ordered his men into the shelter of two nearby bunkers. He then requested the artillery to place VT directly over his positions.[122] The volleys of overhead fire and effective Marine small arms fire then forced the enemy to call off his assault. Although the exact number of Chinese casualties could not be determined, the new fire technique fully accomplished its purpose--repelling the enemy force. [122] The artillery regiment had earlier developed the “box-me-in” fires for outpost defense. If under heavy attack the outpost could call for these pre-planned close-in fires that completely surrounded the position. In event of radio or wire communication failures, the outpost could call for “box-me-in” or “Fire VT on my position” by signal flare or other pyrotechnic device. _Henderson ltr II._