Unlike the phantom tunnels, the trenches were very real and served as a constant reminder of the enemy's intentions. These networks were quite understandably a source of concern to the defenders who watched with fascination and no small apprehension as the trenchlines drew closer and closer each day. Working at night or under the cover of fog, the North Vietnamese often moved their lines forward as much as 200-300 meters at a time. There were several methods used to counter the trenches with artillery and tactical air strikes being the most prevalent. Lieutenant Colonel Hennelly's batteries provided constant fires during the night especially to the east and southeast where the heaviest enemy siegeworks were concentrated. The VT-fuzed ammunition with its deadly airbursts no doubt hampered the enemy efforts considerably. During the day, attack aircraft hit the trenches with every type of aerial ordnance from 20mm cannon fire to 2,000-pound bombs. At night, TPQs were run to within about 250 meters of the wire while Mini and Micro Arc Lights were targeted from 500 to 1,500 meters.(177) In addition, the Marines along the perimeters concocted their own schemes which added to the displeasure of the enemy. During the day, Lieutenant Colonel Wilkinson's men registered on the close-in trenches with their M-79 grenade launchers; these shotgun-like weapons fired a 40mm projectile to a maximum range of about 375 meters and produced a frag pattern approximately 5 to 10 meters in diameter. At night when the North Vietnamese were digging, the Marines periodically lobbed these rounds into the trenches and disrupted the sappers.(178) In spite of the harassment, the NVA launched several attacks against the base from the trenchlines during the last 10 days in February. At 1245, 21 February, the North Vietnamese fired 350 mortar, rocket, recoilless rifle, and artillery rounds into the eastern sector and followed up with a company-sized probe against the 37th ARVN Ranger Battalion. The enemy troops, however, did not attempt to close with the South Vietnamese and, after a distant fire fight, withdrew at about 1500. Although no body count was ascertained, the Rangers estimated that 1/13 artillery and their own defensive fires had claimed from 20 to 25 of the enemy. Six Marines from 1/26 and 18 Rangers were wounded during the encounter.(179)